Run HD tune on the disk
http://www.hdtune.com/files/hdtune_255.exe. Make sure to select the proper disk from the drop down at the top then go to the error scan tab and run a long test. Take a look at the health tab, should give you a good picture of the drives health.
Edit: thinking more about this it may be that you have a single rail on one PS overloaded. I'm not sure about your power supplies but many have 2 or more rails per PS these days.
Edit2: Nope, my stupid. I didn't actually look it up first, that PS has a single 12v rail.