I've never seen a HD with those symptons, but i suppose it is possible. I'm would at first go down the power supply route, you say you've checked it with a different power lines from the PSU with no difference. What about unplugging your slave HD and DVD/CD Drives/ floppy drive etc so no power is going to them. basically all thats being fed from the PSU is the board and the potentially faulty HD. Does it work now?

Also I'd be wanting to try the HD in another PC, just chuck it in as a slave on a mates PC if you can, does it have the same problem or is it fine?