Im inclined to agree about a power supply problem, I had similar problems when I (nearly fataly) discovered my power supply was on the way out. I noticed my fans had stopped, just in time before things heated up. I discovered a 12V power loss. My general rule is, if things start going wrong for...
I had one of these power supplies after discovering my 450W psu was not capable of running the fans, ATI radeon 9800pro GPU 2 hard drives, dvd RW rom, and ATI athlon 3200 cpu in my custom machine. I tried the hiper 580w cos it looked funky, and thats all this thing has going for it, im sorry...