Games don't run as fast as they should (I think)

[Recon556]

Hey guys, I built this machine October 2010:

Core i7-870 2.93 GHz
4GB G.Skill Ripjaws 1333Mhz
ATI Radeon 5870 1GB
850W Corsair PSU
Samsung Spinpoint F3 1TB
Some Gigabyte MOBO (can't remember exactly what it was.)

Anywho, this has been going on for a while now.

When I first put this machine together, I could run Battlefield: Bad Company 2 at max settings at 1920x1080 with no sputtering. Now it sputters off and on. I chalked this up to Lag.

But I just purchased The Elder Scrolls V: Skyrim, and it auto-detected my settings for high, and for a while it ran okay, with sputtering once in a blue moon, but now I am running on medium and it constantly sputters. I can't figure it out.

One of my friends has a similar setup, same GPU. The difference is he has 8GB of RAM and an i5-2500k.

Any idea what's going on?

I don't know what it could be, but it seems strange that this machine used to plow through almost anything, and now it struggles. Thanks for any assistance!

(I didn't know where to post this, so if I need to re-post somewhere else, I understand.)

 

[tusakano]

Have you done FULL virus scans? (Full, not quick scan)
Have you defragmented recently?
Are you one of those people that never, ever, ever turns off their computer?

 

[Recon556]

I haven't done a virus scan in awhile.

I defragmented the day before I got Skyrim.

I turn my computer off every once in awhile. I will do that now and see if performance improves, as well as running a virus scanner.