Video card artifacting and blacking out?

Hey, I have recently built my computer myself and every thing was at first fine, I'll list my PC specs below.


Processor: amd Phenom 720 OC to 3.2 ghz
HardDrive: WD 320GB
VideoCard; TWO Ati radeon HD 4830's in CrossFireX
MotherBoard: Asrock A780GXE
Powersupply: 750W Cooler-master real power pro.
Case: cooler-master RC690

Ok so when I play any game at all I get blinking artifacts all over my screen like little purple dots, it doesn't happen very often though. It seems like most of the time it happens when I'm not even in a demanding 3D game, I could just be playing WoW and it would happen.

well it happened this morning so I turned the game off, checked my temperatures and the bottom video card was 48C, and the top was 68C.
Then a few seconds later my screen completely blacked out and turned back on 4-5 seconds later, I was missing the entire bottom part of my screen (start bar and icons time and stuff) then it blacked out again and turned back on, and it did it about 4-5 times untill I restarted my computer.

I think the top card might have gotten damaged because I used to play crysis and I didn't realise it but the video cards would start artifacting and then I would close the game to see the temperatures and the top video card was as hot as 80C which is far too hot. the bottom video card was only 58C or so though.

The reason why the top video card is so hot is because they are practically touching each other and the top video card sucks in all the hot air from the bottom video card and makes it even hotter.

And I just reinstalled my video card drivers too.

Thanks.

*EDIT* forgot to mention, my video cards idle at 40C and the top one at 49C, and the top one is usually 68C when gaming, bottom is 55C or so.