Sorry for a long post but please bear with me and help me if you can. (i think it's a hardware problem)

Recently a couple of my games (namely Bioshock and Dark Messiah) and even a modeling program (Zbrush) are experiencing video stuttering problems (runs smooth for about 5 seconds then freezes for a second repeatedly), but ONLY during gameplay. Cut-scenes and videos are fine, and even when i'm just standing still in the game, as is regular tasks like working in desktop, surfing, etc. VERY FRUSTRATING. I have tried the following solution from the web with no results:

- adjusting video settings and resolutions in the games including Vsync
- tried 4 nvidia card drivers including the latest one (though i don't know which is optimal for my card)
- exiting all non-essential programs in the background including virus scanner (even cleaned up my startup from msconfig)
- downloaded latest directX (not dx10)
- dusted inside my pc with the air-dusting thingy
- did a registry, spyware and virus scan/cleanup as well as defragged my HD, freed HD space.
- yelled and threatened my computer while bashing my head with my keyboard

I then installed two older games (Medieval 2 total war and Unreal 2k4) to see if the problem persists and discovered something interesting. Instead of stuttering/pausing every 5 seconds the program "slides" for both games. Basically, If i take my fingers off the keyboard at exactly the right time (every 5 seconds) my character/camera on screen continues moving as if i hadn't (with no lag whatsoever). Running unreal 2k4 windowed showed me that happens when my cpu usage spikes in task manager (which happens every 5 seconds). Same thing with Bioshock/Dark Messiah stuttering. This lead me to believe that its a processor problem (but i'm no expert). I've also tried these solutions:

- setting single cpu affinities
- installing latest BIOS driver
- installing a hotfix (KB896256) from microsoft having to do with dual core processors and service pack 2 not working together or something (whatever it didn't work)

Unfortunately that's as far as my computer knowledge has lead me. What really annoys me is that i never had this problem up untill about a week ago. Zbrush , Tomb Raider and Medieval 2 ran fine (on max settings). I couldn't think of any particular event that may have triggered this other than installing Bioshock, because that's when i got stuttering (although i can't be sure, as i hadn't played a game for over a week before that). The computer actually started working fine yesterday (i had my hopes up...), but today it's BACK.

Regardless, here are my specs:

- Windows XP Media Centre Ed.
- Intel Viiv dual core 3.00 GHz
- 2GB RAM
- Geforce 7800GT video card
- 300 GB HD with 150 free left

I'm at the end of my wits. Any help would be appreciated.

I have discovered that this problem is widespread. I tried a flash game. Same problem. Typing. SAME PROBLEM. Probably other things as well. Every 6.2 seconds to be precise. But it only stutters if a have a key pressed exactly at 6.2 seconds. Hence the typing. Mouse is fine. Both are connected wireless, however i doubt a keyboard could be causing actual frame stutters in games. Looking at cpu usage history in task manager as I'm typing, it looks like a freaking heart beat.

I must have posted this in like 10 different sites. If this is the one that solves this first, i swear i will tell the other 9 about the wonders of pchelpforum.com

Can anybody help me?