XPS 13 will only boot with F12

Go into your BIOS setup, then find the boot mode option where you'd choose Legacy or UEFI.  Keep it at UEFI, but choose "Add Boot Option".  Select Partition 2 of your main disk and navigate to the file \EFI\Boot\bootx64.efi.  Save that as your boot entry and you should be fine.  Evidently a BIOS update released for some systems a while ago wiped out the UEFI boot entry list, so it just has to be manually recreated.

Ok, I got home and checked my wife's XPS 13 9350, which also has Windows 10 Fall Creators update, although it does not have a Dell diagnostics partition because I performed a clean install a while ago.  Below is a screenshot of her UEFI boot order, and I apologize, bootmgfw.efi is the correct file for the Windows Boot Manager; I was thinking of the file for WinPE, Windows Recovery, etc.



The second entry with the SSD name in it has identical File System List and File Name fields, so that one could probably even be removed.  This system boots normally even in UEFI mode with Secure Boot on.  Additionally, when I click "Add Boot Option", I too see the same PciRoot path that you do, but when I browse for a File Path, there's a "File System" dropdown at the top, which changes between the FAT32 partitions that exist on the disk.  If you didn't experiment with that before, see if changing the default selection still allows you to find a Bootmgfw.efi file, which would be a file on another partition, possibly the correct one for booting Windows rather than the Dell Diagnostics.

If you still aren't successful, I'd be reluctant to suggest other options because while they may fix your system, they may also render it completely unbootable; the risk simply isn't acceptable for troubleshooting via online forum on something like this.  Based on what you've described, it sounds like something either in your boot files and/or UEFI firmware configuration went wrong.  Did this behavior occur immediately after performing that Windows update, by any chance?

If you ended up in a hardware diagnostics environment, then the bootx64.efi file you chose was from the Dell OEM Diagnostics partition, not the Windows EFI partition.  The Windows troubleshooter wizard is loaded automatically if Windows has failed to load twice in a row or if you boot (deliberately or accidentally) directly to the Windows Recovery partition.  A default Dell system configured for UEFI booting will have the following partitions, not necessarily in this order:

- Dell Diagnostics

- Windows Recovery

- EFI

- MSR

- OS

- Possibly a second Recovery partition because of quirks of how the Windows 10 updater works.

The fact that you couldn't select Partition 2 when adding a boot option is strange, as is the fact that you evidently have to enable Legacy boot mode and then you STILL choose an option under the UEFI section of the F12 menu, even though choosing UEFI mode doesn't allow the system to boot properly.  If you can, experiment with the following combinations of settings, which you'd have to configure in the BIOS:

- UEFI boot mode, Secure Boot disabled, Legacy Option ROMs disabled
- UEFI boot mode, Secure Boot disabled, Legacy Option ROMs enabled
- UEFI boot mode, Secure Boot enabled (this is the default and recommended configuration, and it automatically disables Legacy Option ROMs).

It would also be great to learn more about your disk configuration, i.e. whether it's set up as GPT or MBR and exactly what the partition map looks like.  If you can, while in Windows, open an elevated Command Prompt and enter the following commands, then copy/paste the entire Command Prompt session into a post:

diskpart
list disk
select disk 0 (assuming 0 is your system disk)
detail disk
list partition

It didn't work, I'm afraid.

Setted in UEFI:

Without F12:

• • \EFI\Boot\bootx64.efi you suggested will send me to hardware diagnosis test, that found no issues but no bootable devices neither. I must note that I found no option to select Partition 2 when selecting \EFI\Boot\bootx64.efi 
  • The  "UEFI [...] Samsung 256GB, Partition 2" option will start a dell logo black screen with "diagnosing your pc" reboot cycle.

With F12:

• • Both will send me to the windows troubleshooter, that asks me to choose a language and then show some options (restore, boot troubleshooting, etc). None work so I finally have to choose shutdown.

In Legacy:

Without F12: Black screen "No device found"

With F12:

• • "UEFI [...] Samsung 256GB, Partition 2" will start windows normally
  • \EFI\Boot\bootx64.efi white dell Support Assist screen with a red cross and no message.

If it helps, I checked the "UEFI [...] Samsung 256GB, Partition 2" option and it points to a "\EFI\Microsoft\Boot\bootmgfw.efi" file and it's file system list looks like "HD(2GPT, numbers)"

However, when I try to create a Boot option, the file system list looks like "PciRoot(0x0)/Pci..../Sata.../HD(2 same numbers as above)"

It's in spanish! I hope it's not a problem. I'll try the combinations in a moment

C:\WINDOWS\system32>diskpart

Microsoft DiskPart versión 10.0.16299.15

Copyright (C) Microsoft Corporation.

En el equipo: DELLXPS13-LAURA

DISKPART> list disk

 Núm Disco  Estado      Tamaño   Disp     Din  Gpt

 ---------- ----------  -------  -------  ---  ---

 Disco 0    En línea        238 GB  1024 KB        *

DISKPART> select disk 0

El disco 0 es ahora el disco seleccionado.

DISKPART> detail disk

PM951 NVMe SAMSUNG 256GB

Id. de disco: {74237A17-E483-4D2A-A9E0-F816B644B7C4}

Tipo        : NVMe

Estado : En línea

Ruta        : 0

Destino     : 0

Id. de LUN  : 0

Ruta de la ubicación: PCIROOT(0)#PCI(1D00)#PCI(0000)#NVME(P00T00L00)

Estado de solo lectura actual: No

Solo lectura       : No

Disco de arranque  : Sí

Disco de archivo de paginación  : Sí

Disco de archivo de hibernación  : No

Disco de volcado  : Sí

Disco en clúster: No

 Núm Volumen Ltr  Etiqueta     Fs     Tipo        Tamaño   Estado     Info

 ----------- ---  -----------  -----  ----------  -------  ---------  --------

 Volumen 0     C               NTFS   Partición    237 GB  Correcto   Arranque

 Volumen 1         Recuperaci  NTFS   Partición    450 MB  Correcto   Oculto

 Volumen 2                     FAT32  Partición    100 MB  Correcto   Sistema

 Volumen 3                     NTFS   Partición    788 MB  Correcto   Oculto

DISKPART>

When adding a boot option, I only see FS0: listed in the file system drop-down, so I guess no luck there neither. It did start after an update, but both windows and dell updated things that time so I'm not sure which one went wrong.  If you have any other suggestion I'll try, or maybe better just to leave it as you said?

If you think I should leave, could this be dangerous and make my computer unbootable suddenly or something? Should I contact dell?

Leaving it the way it is would simply be an inconvenience.  It won't make it more likely that something else will break it even more.  It won't make that LESS likely, either.  So I don't see any reason to contact Dell, and even if you did, they'd probably just tell you to back up your files and perform a clean reinstall.  That might not be a bad idea anyway, although that can obviously be a lot of work especially if you have a lot of applications.

The only other idea I have is below, but read this first.  The command below will update the boot files stored on the EFI/System partition (the 99MB FAT32 partition you saw in Diskpart) AND it will add a boot entry to your system's UEFI firmware pointing to that partition.  Windows Setup runs this command automatically as part of a clean install in order to set up new systems.  As I said in my earlier post, this may completely fix your issue, and although I don't EXPECT it would make anything worse, since I can't say that for certain because I don't fully understand your system's current configuration because it's behaving in a way I've never seen before.  So if you want to be completely safe, you may want to capture an image of your system before proceeding.  Macrium Reflect is a popular tool for this purpose, and it has a free version and a variety of paid versions, but the free version will work for this purpose.

If you decide to proceed, open an elevated Command Prompt within Windows and enter this:

bcdboot C:\Windows

I tried the combinations with no luck, all of them including with or without F12 and  "\EFI\Boot\bootx64.efi" or  "UEFI [...] Samsung 256GB, Partition 2" will send me to the dell "trying to repair" and then windows troubleshooting

And ok, based on your diskpart output, your system is definitely a GPT disk, and it has an EFI partition, so having your BIOS set to UEFI mode with Secure Boot enabled should absolutely allow the system to boot, at least via the F12 menu.  There shouldn't be any reason you would need to drop to Legacy mode or disable Secure Boot, so if you have to, then something else is wrong.

When you see the F12 Boot Device menu, you should see an option for Windows Boot Manager.  It seems for some reason, possibly the one mentioned earlier, that file is missing or has been changed.  

The Diskpart command is better for me if I use the lis par (list partition) command which shows all the partitions in the correct order.  But you do know the OS partition is C which is used in the bcdboot command mentioned.

Another command you can use to check the system is bcdedit.  It will show your BCD Store and how it is set up.  If you want to see the entire listing, use bcdedit /enum all.  You can copy and paste at least the basic bcdedit listing.

The bcdboot command will put new boot files in the EFI system partition and should allow you to see the Windows Boot Manager during your next boot.  

Another command you might try first is bootrec /rebuildbcd  but this command has to be run from boot media like install or recovery media.  If it finds a Windows install, not already listed in the BCD Store, it will allow you to add it.  You may need to run this one to get the recovery options back if they get lost during the process.

Most of what I bring up has already been mentioned.   I would like to see the bcdedit listing in case we could modify it to get it back to normal.

I have the same symptoms in XPS 13 9650 after dell updated the bios but i cannot enter "legacy" nor use the F12 to invoke the boot source. the system does not boot as well form a recovery USB

I don’t think this is a BCD problem. The fact that the system won’t boot with the standard BIOS configuration for UEFI and always requires F12 even with an unusual configuration suggests that this is all a UEFI problem. I’m just relying on the BCDBoot command’s fixes to the other areas to maybe fix this, not its core function of modifying the BCD itself.

I also asked about list partition but forgot to add that initially (I thought detail disk showed that), and the OP responded without having seen my edit. But based on posts since then about there only being one file system in the boot menu dropdown, I doubt seeing the partition map at this point would be useful.

@jphughan Thank you very much for your help, sadly bcdboot C:\Windows did not work either. I do see a Windows Boot Manager though it points at the same file as "HD(2....)" and same results. And I did miss your edit, sorry, this is the list partition:

DISKPART>  lis par

 Núm Partición  Tipo              Tamaño   Desplazamiento

 -------------  ----------------  -------  ---------------

 Partición 1    Recuperación       450 MB  1024 KB

 Partición 2    Sistema            100 MB   451 MB

 Partición 3    Reservado           16 MB   551 MB

 Partición 4    Principal          237 GB   567 MB

 Partición 5    Recuperación       788 MB   237 GB

@Saltgrass Hi! Thank you for the suggestion. As stated above I do see a Windows Boot Manager pointitng at the same file. Here I have bcdedit, hope it helps, I may copy the enum all too if needed. I'll try  bootrec /rebuildbcd  and come back.

C:\Windows\system32>bcdedit

Administrador de arranque de Windows

----------------------------------

Identificador           {bootmgr}

device                  partition=\Device\HarddiskVolume2

path                    \EFI\Microsoft\Boot\bootmgfw.efi

description             Windows Boot Manager

locale                  en-us

inherit                 {globalsettings}

default                 {current}

resumeobject            {b7e8fb50-bf56-11e7-ba8f-93fa635d2444}

displayorder            {current}

toolsdisplayorder       {memdiag}

timeout                 30

Cargador de arranque de Windows

-----------------------------

Identificador           {current}

device                  partition=C:

path                    \Windows\system32\winload.efi

description             Windows 10

locale                  en-us

inherit                 {bootloadersettings}

isolatedcontext         Yes

allowedinmemorysettings 0x15000075

osdevice                partition=C:

systemroot              \Windows

resumeobject            {b7e8fb50-bf56-11e7-ba8f-93fa635d2444}

nx                      OptIn

bootmenupolicy          Standard

bootstatuspolicy        DisplayAllFailures

So, I tried the bootrec options in the recovery options that show up when rebooting.

First under UEFI:

/ScanOS or /RebuildBcd didn't find any windows installation
/FixBoot and /FixMbr "couldn't find specified path" 

I switch to Legacy:

/ScanOS finds 1
/RebuildBcd finds 1 and ask me if I want to add it. I say yes: "System could not find specified path"

/FixMbr compleated correctly
/FixBoot "access denied" 

This is completely bizarre for several reasons:

- Your disk is a GPT disk and contains all of the normal partitions that a GPT disk hosting a UEFI system should have, and yet when your BIOS is set up for UEFI booting, apparently it doesn't start.

- Switching to Legacy mode is supposed to prevent UEFI booting, which would mean that the system would only allow booting from MBR disks.  You shouldn't even see any UEFI boot options in your F12 menu while you have Legacy mode enabled.  And yet somehow in your case, you not only see the UEFI option, but it actually works.

- The fact that you can select a UEFI boot option in F12 and successfully boot AND apparently have a Windows Boot Manager entry in your boot list but still can't boot normally is of course wrong.

- And now switching to Legacy mode allowed ScanOS to find your UEFI-based OS even though nothing was found while your system was set up for UEFI.

At this point I would probably just consider a clean install, but if that's too much work, the option I'm describing below might fix this with a lot less effort.  Read until the end, since it's not as disruptive as it may sound at first:

- Capture an image of your entire disk (all partitions) using Macrium Reflect Free.  That way no matter what happens, you can always at least get back to what you have now.  Also build Macrium Reflect Rescue Media and verify that you can boot from it in UEFI mode before you proceed.

- Perform a clean install of Windows 10, which you can do by downloading the Windows Media Creation Tool and preparing a USB stick for this purpose.  Make sure you set your system to UEFI mode and choose the option for the USB stick listed in the UEFI section, not Legacy!

- Assuming your fresh Windows 10 installation boots with your system in UEFI mode AND without needing F12, after you get to the Windows desktop, boot from the Macrium Reflect Rescue Media (in UEFI mode) and choose to restore only your OS partition, not the entire disk.  This will bring back your regular Windows environment, but the fixes to the system partition and UEFI firmware made by the clean install should allow your system to continue to booting normally even after you restore your original OS partition.  If the system doesn't immediately boot after the restore, go back to the Rescue Media and run "Fix Boot Problems".

- If anything goes wrong anywhere above, just boot into Rescue Media and restore your entire disk from the image backup and you'll be back to where you were.