is it The Memory's Fault?

[terror112]

My system:
AMD athlon 64 +3700 1mb L2 @2.6ghz
1GB ddr400
Asus K8M-VM nForce 4
EVGA Geforce 8800GTS 320mb
WD 250GB 7200RPM 16mb Sata-II
EDIT: 500WATT ULTRA PSU (28A)
In games like S.T.A.L.K.E.R most areas bring my FPS down to 5. I Dont know the problem with my PC, but in games that are not very GPU intesive like Lord of The Rings online I get constant loading of the HDD. Would the RAM hurt the FPS this badly or would it be something that causes it like hardware failure? also I know that my GPU should be able to play the game atleast up to 40FPS or more. And my CPU shouldn't bottleneck it very much since it is oced and Athlon 64 is still pretty fast.
HELP ME!!!!!!!!!!!!

 

[XMSYellowbeard]

If it is not a Nvidia driver issue ( do you have the latest drivers?) then you may simply need more RAM. Your HD loading is the Windows paging file being used heavily which means you should benefit from having more RAM.