There may be nothing physically wrong w/ the drives. XP home and Pro and the 2 different HD's likely had some different drivers installed.
Other than a failing drive, I'm not sure what else it could be.
I'm stumped too. As I said the drives were running fine on XP Home on another HDD so I don't see how changing the HDD & OS could harm the drives. I feel like it must be something with XP because even VLC media player freezes. I'll probably have to reformat again. What a PITA.