I hope I'm wrong, but it sounds like that drive may've bitten the dust. You could try putting it in another computer or enclosure to see. If you manage to get it working, I'd sure want to copy anything that's on it to another hard drive. If the drive's bearings have worn out, there's been a head crash, or some other problem caused it to die, the only way you'll get its contents is via a very expensive recovery procedure. Personally I never leave valuable data in just one place because these things can and do happen. Unfortunately Murphy loves technology.

Good luck.