Sorry for the problems you're having.

Sometimes a disk that doesn't work in one machine works in another. That could be caused by the quality of the disk, the error correction on your optical drive or the setting in your BIOS. What is strange, though, is that it worked for a while and ceased working after that. The fact that you can't boot from your USB either suggests the problem could be elsewhere. Maybe someone else here has an answer/suggestion.

BTW, could I ask where you bought the disk. We've not had any complaints so far about the company we recommend here but I do know that quality varies from one supplier to the next.

Can't find KNOPPIX filesystem | Wiki articles