Well, I tried to take the hard drive (the one with my boot info on it; it also has most of my personal files) and install it as a slave on my girlfriend's computer, and it did the exact same thing.
Wouldn't even spin up. So, I tried a different hard drive that had not been tested on the new system, and it spun up and is acting normally. This other hard drive also has my personal files on it; I'm now copying them onto my girlfriend's computer's drive.
However, something still seems fishy here...doesn't seem like the drive would have just picked right then to go out, and again, as far as I know, the jumpers are set properly. I haven't tried the 80GB on my girlfriend's computer; if that one doesn't spin up either, then what could the problem be? The power supply with the new case is set up at the same voltage...could there have been a power spike of sorts?
Ugh I think I'm gonna be sick...if there is a power supply problem and my brand-new 80GB drive was damaged by it...