Wierd Problem with my video cutting out

Ok So today I was playing Halo and my screen turned black and the light on my montior went from blue(on and showing video) to yellow(stand by or computer off) but I could still here sounds from my computer and I hit alt-tab and the sounds stopped meaning I alt tabbed outa Halo. I restarted my comp got to the windows login black screen restart, same thing. Pull my computer out blow so dust out of it replug back the keyboard and monitor cable boot it up and its fine and I play Halo and War Rock for a bit. I then went out and came back it was fine went to watch a movie in WMP10 while it was starting up I picked up y alarm clock(cord goes behind computer) and the screen went black but I still was listenning to the audio of the movie.

My computer is inbetween a big ass closet and my desk so the ventialtion on the sides is crap but it has no fans there ventialtion in the back is fine. Since the Halo incicdent I had the side panel off and it doesnt even feel warm in the case and the vid card fan spins fine and ispushing out cold air

Specs below
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3200+ Venice(stock)
DFI nF4 Ultra-D
ATI x800xl(stock)
1gig Mushkin DDR400 3-3-3-8 @ 2.5-3-3-7
CoolerMaster Centurion5 Forton 400watt
160gigWD IDE LiteOn CD/DVD burner
Hyundai L90D+
Warning the back case fan of the Cent5 hits the onboard sound board on this mobo, if you buy the above combo get out your dremel. Also my motherboard didnt like my cheap ram and I had to make the timings 3-3-3-7 for it to work.
Diddy says "FOld or Die"