I want to know if this is due to my Nvidia GT 9500 1GB

So Everytime i play any 3d game my monitor screen shakes back and forth and blinks and sometimes turns off my monitor if i dont close the game fast. Is my video card messed up or is it my wattage supply its at 420

xtra info
4gb ram
this doesnt usually happen when i surf web or watch videos just when gaming