You are perhaps using a DVI cable with your flat panel display... I (and others, before and after me) has posted threads about this problem. Search for DVI or psychedelic colors or similar to feel less alone with the problem.
Then, my suggestion is to post a bug to nVidia since the more bug reports the greater effort they ought to put into trying to fix it, quick!...
The only workaround seems to be to use a VGA cable, it works but with a bit worse quality.