First, open your pc and take a look at all the capacitors on your motherboard. Any goo, bulging tops, indications of a leak . Go to http://www.badcaps.net/
they have quite a few pics of what badcaps look like. If you have these you need to replace the caps or the motherboard.
If that checks ok; Go to your hard drive manufacturers website, download and run their DOS level diagnostics. they might have a utility to read the SMART built into your drive; if so use it and see if the drive has detected anything wrong with itself.