"You won a Hugo Award?" he gasped, at which I explained that mine was only a display copy; one of two left over after the 2002 Worldcon.
Getting back to the issue at hand, he finished reinstalling the motherboard and, after much fussing with the connectors to get the screen to start working again, booted the machine from a known-good-clone. (I'd cloned it from the other computer, and the drive would boot in the other computer as well.) It seems to be working okay now. We'll see if it stays that way. The technician couldn't believe the symptoms I reported -- having it be a hardware problem with the computer corrupting hard drives seemed so improbable. Well, I agree, but with all of the other likely causes eliminated, it seemed like the only other thing left.