As you do not mention to many details I will try and fill them in. Your running XP,your graphics card is a HD 4850 if my memory serves, and the game you might be having problems with is Skyrim? How am I doing?
Have you tried dropping the resolution down to 1360 x 768 whilst gaming and see if your game still crashes. Check that your graphics card's fan is free from dust.
Why do you have your monitor set at a resolution which is lower than its recommended,there are other ways to make everything easier to see if you are having problems viewing,my good lady has sight issues and I have had to do the same to her PC to enable her to be more comfortable.