You cannot format in another machine and put back.

BIOS has to be set Secure boot OFF for F12 to work.

Thanks for the reply

I thought if Windows was installed it would be formatted UEFI so would not need to be  set secure boot off.

unfortunately, I can't get into bios to turn it off If I knew where the battery was I could remove that to reset bios and then I would be able to get in.

When I posted I got an email from Dell asking for express code I put it in now it saying: -   ESC  

I formatted windows to latest format put drive back in XPS and it booted first time when it did not boot it was formatted mbr.

still can't get into bios but now no need too

Thanks

Maybe try holding the Fn key while pressing F2 or F12 if your keyboard is set to default to the multimedia functions on those keys rather than the F key functions.  I thought those keys always worked as F keys during initial startup, but maybe not.

In any case, speedstep above is incorrect that Secure Boot has to be off for F12 to work.  I access the F12 menu with Secure Boot enabled all the time.  You can always access the F12 menu itself regardless of Secure Boot's state or even Legacy vs. UEFI.  And you can actually boot from a device listed in that menu while Secure Boot is enabled as long as the device you're booting from has been set up correctly for UEFI booting and contains an OS that has a signed bootloader, such as Windows 8 and above and certain Linux distributions now.

Using another PC to install Windows onto your disk is a bit unconventional, but it will work as long as you boot your Windows install media on the "transplant" system the same way the actual system will boot (Legacy vs. UEFI mode) AND you do NOT let the "transplant" system actually boot from that disk for the first time.  You need to let Windows Setup run through the initial phase, but when it gets to the point saying it's going to reboot your system, you need to shut it down instead.  The reason is that the first time you boot Windows from the internal disk is when it runs the "sysprep specialize" phase, which customizes the base Windows image that Windows Setup put onto the disk for your specific hardware, so that should always occur when running from the system you'll actually be using that disk with.

If your disk was formatted MBR the first time, it's probably because you booted the Windows installation media in Legacy mode.  Windows decides how to install itself on a disk based on how the installation media itself was booted, so if you want a UEFI Windows installation, which includes a GPT disk, you need to boot your install media in UEFI mode.

Thanks for the reply

When pressing either F2 or F12 with or without holding the FN key it will only boot from H/d 

The first time I did it with a donor win7 vintage, MBR did not boot, tried another newer donor EUFI  just before the first reboot I turned it off switched H/D to XPS Dell and it booted from H/D and finished the install and activated.

I think if I could have unplugged CMOS battery maybe it would have reset bios then F12 might have worked

I believe M/B has to be removed for this.

in any case, does not matter now as the customer has got it back working and she is happy

I was reading a similar case with same laptop Dell tech came on site he changed Motherboard to fix the problem

in my case, it was long out of warranty.