Hello,
I have a problem with unlocking a bitlocker-encrypted drive with TPM 2.0 by running the manage-bde -unlock -password command in safe mode. The disk is locked with a PIN that I know. After entering the PIN, the message "the password failed to unlock volume" is displayed. I do not have a recovery key. The PIN is definitely correct because I logged in using it. After changing the BIOS, I cannot start the system, a recovery key is required. I made a logical copy of the encrypted partition early on. I have access to system files. I cannot find the .BEK file in this partition. Do you have any idea how to unlock the partition and log in to the system?
Is the disk in the original system with the TPM when you're trying to unlock it? (if not that'll be why)
Was the TPM cleared? (Changes to the BIOS shouldn't necessarily - but obviously could)
Are you using manage-bde -unlock C: -password ? (you didn't mention the drive letter so checking you're pointing it at the right drive letter - whether C: D: or something else)
You don't need to boot the system necessarily to sort it out but you'll need to use it to unlock the disk (if you haven't got a recovery key and can't get one - have you checked online: Finding your BitLocker recovery key in Windows - Microsoft Support )