Why does my computer run slow and get low fps when i play a game?

[mathewsgordon]

I just recently upgraded my computer and it is pretty good but its is 10x better than ,my brothers and he is able to Alt+tab outa battlefield 2142 and he gets higher Fps than I. My setup is this: AMD athlon 64 3800+ dual core processor, Abit kn9 ultra, nvidia gforce 7900 gs Pci express and i got a new power supply too. My brother computer is just a 3000+ amd athlon with a 7600 gt agp and idk what mother board. But my computer is NOT overheating i have already measured and tested that thery if anyone has any other idea please tell me thanks a bunch

[Lunarsight]

I am venturing a guess here, but you may not have your Windows settings optimized for gameplay.Under Control Panel/System Properties/Advanced tab, double-check the various settings related to the Performance section there. Once in Performance options, click on the Advanced tab there, and check those settings as well.

[globeweasel]

stop some other programs from running