games keep crashing

i wonder if anyone can help me i have put a geforce 2 in my computer and upgraded from 98 to windows xp pro ever since then every time i load a game i get 5 minutes play then the game crashes some times it says that the game exe as encountered a problem and as to shut down and some times the game just quits and i return to desktop and some times my computer resets anybody got any ideas as im getting really annoyed at this please help