Don't Panic
One cause may be a dead CMOS battery and the BIOS reset to default.
When the following is done:
Running bcdbppt does two things: it refreshes the boot files just in case, and more importantly, it forces the motherboard to write a brand-new UEFI NVRAM bookmark pointing straight to your Windows drive.
F2 and check the BIOS. If it's set to Legacy and Raid instead of AHCI and the date is somewhere in 2007, the battery is probably dead.
Window's 11 can run on legacy boot but it's a little risky and doesn't always work.
What to do.
1. Install a new battery
2. Create a Windows install bootable flash drive.
3. Open the Gemini app on your phone and tell it what is going on.
You are all set. Do what it tells you to do.
Good Luck
Gemini and I fixed the boot sector and BIOS settings once. I noticed the date problem and reset it but didn't' bother replacing the battery. In the old days we could just F1 and continue to boot. Those days oar over. After a fer weeks it happened again. I had to do it all over but this time I replaced the battery.
Ventoy Hint
I dropped a downloaded Win.iso onto Ventoy. I would not boot in standard mode. I had to use Wim-boot. It loads everything into memory and boots.
Here is the entire process:
Windows Can't Find A Boot Drive
(This assumes Windows was installed as UEFI boot before the failure).
Boot to BIOS
(usually F2)
Check if set to:
Windows Boot Loader
UEFI
AHCI (Don't worry if changing from RAID. Change it. Win11 will handle the change)
Determine the volume number of the EFI partition
(Drive letter may not be the same as when the PC is booted).
Boot to Wininstall.iso from a flash drive. F12 launches boot selector in Dells.
At the first screen:
Shift + F10 for command prompt launches cmd as Admin
diskpart
list volume
You are looking for a FAT32 of 100 MB - 500 MB
Let's assume the volume of the EFI is 3
In diskpart do this:
select volume 3
assign letter=S (The EFI partition needs a letter to accept being written to)
exit
Exit is needed because the next commands are in command prompt
bcdboot D:\Windows /s S: /f UEFI
To remove the volume letter do this:
mountvol S: /d