Strange problem occurs whenever I try to play a game....

So I just got a new computer and whenever I play a game a weird horizontal green line appears and a thick green line appears vertically. It probably has to do with my video cards (2 Nvidia GeForce 6600 GT's), i'm guessing there's an option to turn them off, but I can't figure it out.

Someone please help me!
 
Thank you very much sir.

Now if you'll excuse me I'm off to play F.E.A.R. without some weird green lines.
 
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