Lagging System During Full Screen Games

Hello,

Recently, when I run a full screen game like Unreal Tournament 2004 or even Starcraft, my cursor lags too much to do anything but barely reach the exit button. My system ran these games perfectly up until a couple days ago. Nothing has changed since then. My specs are as follows:
Intel P IV 2.4C
Asus P4P800-E Deluxe
512MB Corsair DDR-400
80GB Seagate SATA150
ATI Radeon 9800 pro
I know I should probably upgrade my ram to run UT04, but what troubles me is that it started happening all of the sudden, and even to an old game such as Starcraft.

Thanks in advance for any help.

Atomic Ferret

Interesting, did you experience a crash or install anything around the time of the slowdown? Don't think a PC would just start acting up like that...

My system has not crashed ever as far as I can recall. I installed AutoCAD recently, but I don't know what that would have to do with anything. I scanned my system for spyware and viruses and came up with nothing.

download avast antivirus...avast.com
download search and destroy...not sure on link
then uninstall and reinstall your mouse...get specific drivers if possible.
this seems software related for sure since no hardware changed.

Physically check your 9800 pro. Maybe there is a heat issue. I know the fan on my 9700pro just fell off one day. Didn't notice till I kept crashing in games and decided to peek inside.

I have AVG antivirus and ran virus checks.
I have Spybot and I have run scans.
I checked my video card, it is fine. My fan stopped spinning a few months ago and I RMA'd it, but it's fine now.

After today I have realized that ever one of my programs is lagging, but some not as much as others. Maybe I'll back my stuff up and reinstall windows. I don't know what else I can do.