Windows 7 Graphics Corruption

Whenever I boot up windows 7 with both my monitors connected I get a corrupted screen on my main monitor, my other monitor works fine. My main monitor shows blue and white lines that flash, this changes depending what is on the screen. Windows logs in and I can see that mouse on my second monitor. I messed around with the screen resolution (I managed to get the screen resolution window on to the second monitor) for a while but changing it did not change anything.

After that I changed my main display to 16bit and and the screen started working! I changed it back to 32 and it continued working absolutly fine. When my main monitor is showing the corrupted screen I can printscreen and see my whole dekstop perfectly. I am very confused about what is going on. I have swapped round what port each monitor is connected to and the same thing happens. I get the same problem when trying to play games and can get out of by changing to 16 bit and back again.

I have been using both monitors on XP for almost 18 months with no problems. My graphics card is a 7900gs, my main monitor is a 22" LG LCD running at 1680x1050 and my secondary monitor is a Samsung 15" LCD running at 1024x768. i can try to get a picture of what happens if anyone wants to see. Anyone having this problem or know a way to fix it? I am having problems also with aero crashed, see my post desktop window manager craashing.

Thanks