Another possibilitly is that some program you're using (like a game) is changing the resolution and then not changing it back when it exits. I've see Rome:Total War do this once or twice, for example. To fix that, I changed my windows screen resolution and game resolution to be the same. That way it wouldn't mess things up when it didn't work right. Not sure what the root cause was. All drivers, directx, etc were up-to-date.
Gary Swift (aka gswift)
Lenexa, Kansas USA
You can try to monkey-proof your program, but you'll never monkey-proof the monkey.