OK, this is probably a hideously ignorant question, but I'm stumped. I have a computer with a hard drive that won't spin up . . . or will it? If I plug in the power cable but not the ribbon cable, it spins. If I have the ribbon cable plugged in, it doesn't. What the blue crap?
I think there is some board complaint in your HDD, probably a short. Another chance is with the IDE cable. Replace your cable and try again...