it sound heat related to me, after 10 or 15 minutes u say? do u have a can of air? lol sounds funny eh? compressed air in a can, spray the air around your cpu and fan and housing. also, look at your motherboard, check for swollen capacitors, the top should be flat, not bulged out. if u have enough air, spray some in ytour power supply too. also, acklan could have hit it on the head too, it very well could be ram.
here is a link to show you what a capacitor is, there is many on your motherbaord.http://electronics.howstuffworks.com/capacitor.htm