Well you have a few opitions:
1) The drive is faulty and must be replaced
2) You installed an IDE driver that is causing a conflict with the copy protection e.g. The recently removed nForce 2.42 drivers.
3)Plug the drive into a friends computer and see if it works.
4)Try the drive in various settings e.g.Primary slave,Secondry master etc.
5)Format your computer and reinstall the OS (if you think its a software problem)