Hi, welcome to TSF
Have you tried reinstalling or updating your graphics driver?
Is anything overclocked?
Make a note of the temperatures and voltages in BIOS, then again during fullscreen gameplay with
SpeedFan. Post back with both sets of readings so we can compare the idle and stressed performance. If SpeedFan doesn't show the graphics card temperature (GPU), use the nvidia control panel or
RivaTuner.
What make/model is your PSU?
Do you have any other programs running in the background while playing a game? (antivirus, IM chat, music, etc)