speakers randomly pop

Why my computer keeps turning off?
My computer shuts down any chance. No reboot or an error message, just pop out of my speakers and a black screen. My first assumption was that it was overheating, especially since I have a map Video aftermarket. To remedy this, I opened one side of the case and aiming a small fan into the case. I also pulled away from the wall. However, I now believe that the problem is caused by something other than overheating, as sometimes I can play World of Warcraft (very demanding on video card!) for 12 hours without incident, and other times I'll do something simple like reading Yahoo news, and he died. power source? Virus? Bad driver? What do you guys think?
Could be the dust in your lap. Take the side panel off and cleaned. You can tell when you open it, if a lot of dust.
Don`t Stop; Make it Pop, DJ Blow My Speakers Up Tonight