Hard drive failure is one possibility, another is one or more faulty RAM modules. Both are very common.
You can test both with diagnostic software that loads from a bootable CD, even if Windows isn't installed, it doesn't matter.
Hard drive diagnostic software from drive manufacturers:
http://www.tacktech.com/display.cfm?ttid=287
RAM testing software: http://www.memtest.org/
Please start a new thread if you need help with making a bootable CD from the above downloads.