Software caused system slowdown?

First off, I'm new to the Major Geeks community, so hello to everyone. Now, down to business. I wasn't sure if this should be placed in the games section or in the software, for this involves games, but doesn't really pertain to them exactly. At the current moment, I play 2 games. Call of Duty 2 and City of Villains. A couple of my friends asked me to play CoD2 with them for a bit, so I gladly accepted. We had fun and then they had to leave. Upon them leaving, I exited out of CoD2 and started up CoV. The patcher came up, claimed that there were no new patches, and asked me if I wanted to continue into the game. I left the patcher screen running, for I wanted to indulge in some Fark. After spending about 10 minutes on Fark, I then closed out Mozilla and started up City of Villains. Now usually, at the loading screen, I have sort of a video glitch at the top of the screen where the colors are abnormal, then everything loads and works fine. This time, that glitch was gone, and was replaced by a horrible stutterring of my sound, as if my anti-virus was running in the background. I exitted and check, but there were no memory-hogging programs running. I thought this was odd, so I started up some of my music. Upon startup, the music stuttered a little bit, and then would periodically stutter during the playing of the song. I started up CoV again, and the same thing happened. Upon exitting CoV, my desktop reset itself. This was freaking me out, so I decided to reboot. I get to the windows xp spasl screen and then it takes it about a minute to boot up, which is about twice as long as it usually takes. Then it sits at 2 different black screens- one as if the backlight is on but the screen is not, and then another where it is pitch black, before going to my user selection screen. I began to think it was my DDR Dimms, so I took both out, cleaned them, and then tried again. Same thing happened. I turned off my computer and then put the dimms in the other 2 slots on my mobo. Same thing. If I try to play CoD2, everything works fine until it attempts to load a map, in which case the sound begins to go very slow, as if it were in slow motion and had a stuttering problem. This happened to me before, but my harddrive also started clicking, so I assumed it was the harddrive and bought another, which has been working fine up until now. Any help on this would be much appreciated, and if any more information is needed then I will be happy to submit it.

Windows Xp Pro SP2
AMD Athlon XP 3000+ 939pin
Corsair ValueRam 1 gig pc3200
ATI Radeon x800XT All in Wonder 256mb
Soltek SL-K8T-939FL Mobo

 

Update: I did a system restore to earlier this weekend and it fixed the problem. Any information as to what this might have been and how to prevent it would be greatly appreciated.