Bios on T43p does not modify disk password

[Peter8049]

On my backup T43p, I set the same password for power-on as well as for user and master disk access. When I recently tried to change the disk password in the BIOS setup utility, BIOS reported that the password was changed - but after a warm start it turned out that the original password was still in place! The same problem occurred when I removed the disk password by twice clicking the enter key.

Furthermore windows can't be started. Instead, I get the error message:
A problem has been detected and windows has been shut down to prevent damage to your computer.
UNMOUNTABLE_BOOT-VOLUME

Any idea what happened here and how I can fix this error? Many thanks for your suggestions.

Peter