I agree it can't be the PSU.
Hope you had all your files backed up because your hard drive sounds dead to me. How old is your computer? Much more than 4 years old? My mate's computer is more than 5 years old and the hard drive sounds rather like a lawn mower with random variable speed control. I keep telling 'em his cheap old hardware is going to give up on him someday soon but he doesn't seem know any better.