[Imp]

I would suspect your video card drivers, you dont mention the card but it may well not support 1680X1050 resolution genericaly so its working harder to emulate it & if the drivers are not up to date triping up.
Select screen resolution for your descktop & see if its in the list to see if your graphic card supports it as a native resolution.

On a side note surely full screen at that res gives you a distorted view as its stretched to fit your monitor why not play in windowed mode so the game displays correctly?