now all I get are BSOD's

AHCI and Uefi off.

BSOD... see the screenshot below...

Boot from the USB Stick and then press Shift and F10 to open the command prompt. In the command prompt run the command:

bootrec /rebuildbcd

What do you get then displayed?

Can't find the windows installation see below...

Run the command:

bcdboot c:\Windows /s c: /f all

What do you get then displayed?

Results below...

Try to boot from the hard drive again.

Alas, same BSOD as before (error code 0xc0000225 - NLS data is missing or contains errors, etc...

Okay.
First turn off the computer.
I have to check something.
But I can't do that at the moment.
I come back to you Probably tomorrow.
Please be patient.

OK cya tomorrow.