Monitor keeps going out/comp freezes

So for some reason out of the blue today his comp freezes when he tries to go online on a game and then his comp locks up monitor shuts off. He gets brown and white strips flashing. I am thinking its either one of his grpahics cards dieing or power supply but I don't really know.He has 2 7800 I believe it is. He doesn't know any others but his comp used to work fine but yea just today for some weird reason its been doing that. Monitor keeps going out/comp freezes
What OS is ''he'' using?Update all drivers, run multiple virus/spyware scans, make sure other games work. That's all I know, then come back and ask the other dudes more questions if none of these work or find anything. Monitor keeps going out/comp freezes
Oh this happens with everything he does even when he's not doing anything. He's using XP.
Take one card out, then the other, and see if the problem persists. If problem only happens when a certain card is used, that GPU obviously has a problem. The first thing I would do is buy a can of air and blow out both heatsinks. After he does that, the problem will go away if it was a heat issue (he'll also get noticeably better framerates). If the problem persists after blowing the coolers out, one or both of the cards is likely dying. He was due for a graphics upgrade anyway, so that's as good an excuse as any.