I am having a similar problem. After building my new pc and installing my new OS (windows 7) I am finding now that my screen will randomly scramble while browsing with firefox. Half turns black the other half looks like digital scrambling of snow from a television set. When the problem occurs my dual display doesn't seem to be affected. It usually happens when there is some sort of video playing. If i press a random combination of CTR+ALT+DEL, ALT+F4, and CTRL+ SHIFT+ ESC I can get the scrambling to disappear somehow..it's very confusing.