Inspiron 7786, no bootable devices found, #3

Power up and go into Setup (F2).  What shows in your drives listing?

You're going to need to post as text or as a link, or wait until a moderator approves the image.  We cannot see the image you've posted (and that can take some time).

Did you at some point turn secure boot off?  It should be ON by default unless you changed it.

@ejn63  In F12 Menu:

Boot Mode is set to: UEFI; Secure Boot: OFF; PTT is ON

Other Options:

BIOS Setup

Device Configuration

BIOS Flash Update

Diagnostics

Change Boot Mode Settings

Exit Boot Mode and Continue 

Well is your in UEFI mode Secure Boot should be turned ON, I think somehow your BIOS SATA is set to RAID and your OS does not have the RST driver installed.

What did you do just before this happened? if nothing then your hard drive/SSD may have failed, or the physical connection has been disconnected.

@Clintlgm  I enabled secure boot again. Previously disable to troubleshoot. 

SATA operation is currently set to RAID On. Should it be Disabled or AHCI? 

One day I booted my the laptop and it just ran a system scan in Dell SupportAssist instead of booting up to Windows. 

There is your problem you can't just turn it on and off.

So now you'll have to fix your OS, to do this you'll probably need to Clean Install your OS Windows 10

A workaround is to, If you have a Macrium Reflect Drive Image you can Restore it to solve your issue?

So when you Clean install, if your BIOS will allow you to switch from RAID to AHCI, do it before you start the clean install

So if your BIOS will not allow the switch from RAID to AHCI, then you will have to load the IRST driver during the Install. During the install, you will arrive a the part that asks you to select a volume to install Windows too. Presently you won't see your HardDrive/SSD. However, you will see a link that says I have a driver or something like that. At that point, you will browse to the IRST Driver that you have downloaded to a USB thumb drive, Yep the same on that you are installing windows with. Once you select the RST f6flpy-x64 it will install and then your HardDrive/SSD will be available to install windows to.

Before you start, Remove your HardDrive/SSD and using a USB to SATA or USB to m.2 NVME adapter connect tit to another computer and recover any data that you can't afford to lose.

Then there is this old post in Windows Ten Forum https://www.tenforums.com/customization/104898-switch-raid-ahci.html

I believe since you can not boot to windows you will not be able to accomplish the switch in this tutorial

You can Goggle on other methods to recover your HardDrive/SSD back to RAID or switch to AHCI but I don't think there is any way without being able to boot into windows. 

@ejn63 

Yes, I disabled it to troubleshoot. I have turned it back on. 

RAID ON is the normal as-shipped configuration from Dell.   What storage is in the system - one SSD, one HDD, or one of each -- and in any case, what devices?

@Clintlgm I have downloaded the OS onto a usb thumb drive using Dells website / Dell OS Recovery Tool from my desktop and entering the service tag for the laptop with the issue.  When I boot up the laptop with the thumb drive inserted, it loads OS Recovery. The only choices that I can click on are: scan hardware, backup, and reset/update. There is a repair option but that is grayed out. When I choose reset/update, I get a message that says “We are unable to detect any disks that can be utilized for a cloud restore”

Should I re-try all of the above after switching from RAID to AHCI? 

@ejn63  storage is HDD, Total Storage Capacity 1,000 gigabytes.

If the drive has passed diagnostics, but the system won't boot, you're likely in for a Windows reinstallation.

https://www.dell.com/support/article/en-uk/sln311102/windows-reinstallation-guide?lang=en

Since you disk previously was set up to boot RAID you may have to use DiskPart to clean it. 

I would forget the Dell Recover . Download Win 10 install from Microsoft using the Media Creation Tool (MCT)

Allow the tool to create your USB install media. USB needs to be 8GB and not have any other files as the tool will format it.

On you Dell Support page for your Service Tag number download, all your drivers have them read to install

You would on the Same USB Thumb Drive your install is on create a Drivers Folder have all your drivers there ready to install.

Your BIOS should be Set to AHCI before you start the install