yeah, I ones installed new drivers for my vidcard and all avi's just displayed a green screen. Changed back to the old ones and all was fine again.
But like others said, could be overheating too. I hope it's just the drivers.
I don't think it's overheating, I got the same thing when I installed new drivers, but if you tweak some of the control panel/rivatuner settings it looks fine again. I can't remember which ones though, just try playing around with them a bit.
Sol owns all ! 
But like others said, could be overheating too. I hope it's just the drivers.
But also could be driver related, reinstall/install old ones.
Don't think it's overheating tbh but ..
hf.
EDiT: found the problem http://shaxxer.org/~goochie/chas_hahaha.jpg