Help ..
As @Lehsyrus said , go from the ground up , as for FPS in game with a GTX660+ or a 6850 or bigger you would get as much as there are . The question is irrelevant , build an entire new machine with the specs said by Leh , they are big enough for gaming and everyday use . The one you have is older than the Bible....
buy a new pc 
do you have moni?