Motherboard swap - UEFI boot problem

[RatmanGB]

Hoping someone can help me with this one!

I've just swapped out an old P67 board for an MSI B450 Tomahawk Max II which defaults to UEFI and which seems to mean that everything has to go through the Windows Boot Manager.

Although I've pointed the BIOS at the 2TB SSD with Windows 10 on it, the only option when Windows Boot Manager comes up is the ancient Windows 7 install on an even more ancient 1TB HDD.

I can get the PC into Windows 10 by setting the BIOS to CMS mode which will then boot off the SSD without showing any kind of boot menu, but without being able to use UEFI mode I can't upgrade the PC to Windows 11 (or use ReBAR if I wanted to).

Can anyone suggest how I get the Windows Boot Manager to recognise the Windows 10 installation with the BIOS in UEFI mode?

Thanks!

 

[RatmanGB]

Further information, in case it helps:

Removing the old Samsung HDD with Windows 7 on it and booting via the UEFI Windows Boot Manager (which is pointed at the SSD with Windows 10 on it) causes the PC to try to load Windows 7 and throw a missing winload.efi file error (presumably because the Samsung HDD isn't there?). However, pressing escape causes the PC to load Windows 10 anyway!

This might be very straightforward but it's baffling me.

 

[RatmanGB]

The plot thickens. I put another cheap SSD in the PC and cloned Windows 10 to it so I could mess around with it and not break the PC (it's the other half's and she needs it for work!).

After trying the startup repair option (no good) and then manually recreating the boot files with BCDBOOT... it was still trying to boot into Windows 7, despite that not even appearing as an option under BCDEDIT.

I found EasyUEFI and that DID show two Windows Boot Managers - one on the main C: partition and one where it was supposed to be, on the EFI partition.

Try as I might I can't delete the one I don't want - it just keeps coming back - but I HAVE managed to disable it and the PC now boots directly to Windows 10 with the BIOS in UEFI mode.

Success! Mostly...

This has revealed a new issue - when I put the SSD I cloned Windows FROM back in - that SSD is always shown as the C: drive, whatever drive I point the BIOS towards. Which is weird.