Computer will shut off randomly and won't turn back on for about 15 mins until it turns on by itself. Don't think it's overheating because one, the case side is off and the fans can be turned up, keeping the motherboard or cpu or whatever around 53 degrees or less and I have never had any problems before this. My friends think it's either the power supply or the MB. I was looking for some sort of diagnostic software where I could check both. What's going on??