When was the last time you cleaned out your computer ( i.e. blow out the dust with compressed air/can of air etc ). I have had my cpu heatsink get so much dust on it it stopped airflow and the cpu would overheat and crash all sorts of 3d games, of course like you though, I could browse the web, but nothing 3d game related..
Might be worth a shot looking into. It's a good idea to blow out your computer ever 2 months or so depending on what kind of area you have it stored in ( dusty, dog hair, near a open window etc etc )