I'd follow aircobra19's advice. It may not be the hard drive that's the problem - could be RAM/Motherboard etc., so if you connect the hard-Drive as a second drive on another pc (if you have access to one), this will tell you if the data on the drive can be accessed (Don't try and boot from the drive while attached to the other pc).
Does anything come up on your screen when you do try to start the computer or does it just sit there beeping?!