Could be a motherboard controller issue. This is not repairable.
Try using a different IDE connector. Did you happen to try to "flash" the BIOS of the motherboard? IF so this may also be part of the problem.
The next easy thing to do is to try doing what I said in my first response-power down and disconnect the hard drive completely. Let the box run until you hear the noise. If after say 30 minutes it does not power down or make any noise-you can swapping the power supply and reconnecting the hard disc and see if that solves the problem. Sadly, all of this may be for nothing IF there is a failure of any sort on the motherboard.