Go into your computer's BIOS and see if it'll see the drive (you'll probably have to ``Scan for IDE Disks'' or something similar). If it can't see the drive, then your OS won't, either.

It's possible you've got it plugged up wrong, or (my favorite) forgot to plug the power into it. But if you're sure you've got it plugged in correctly (check both ends of the IDE cable) and your conmputer still won't see it, it's probably simply dead.