Boot computer, BIOS loads, and Windows doesn't.
I get this error message:

So I google it, and find these instructions: Windows RT 8.1 upgrade fails with Boot Configuration error | Annoying stuff I figured out (or am trying to)
I'm up to the bit on entering the CP code, but that's where the problems start.

C:\>bootrec /rebuildbcd
Scanning all disks for Windows installations.

Please wait, since this may take a while...

Successfully scanned Windows installations.
Total identified Windows installations: 1
[1] C:\Windows
Add installation to boot list? Yes<Y>/No<N>/All<A>:a
The requested system device cannot be found.

So I try a different approach. I try 'Refresh your PC'. 'The drive where Windows is installed is locked. Unlock the drive and try again.'

...And 'Reset your PC.' 'Unable to reset your PC. A required drive partition is missing.'

'Start-up Repair' couldn't repair my PC.

I use an SSD as a harddrive, and it was working previously.