So far it has not happened with any other game, only TF2
Combination of issues here: Source is a cranky old piece of shit bodged up to look like a real engine and your card is now 4 generations behind (not an issue in and of itself, rather a potential issue as Nvidia are notorious for cocking up their backward compatibility).
First up, I'll assume you followed the install order I gave you when I sent you Win 7? Right?
If not, then that's your issue. Assuming its not try and update your GFX driver (COMPLETELY REMOVE THE OLD ONE!) and download the latest redist for DirectX and get that installed.
Do you have 2 gig of ram like I guessed in TF2 chat or do you have 4? If you only have 2 a) buy more (match it ffs!) and b) disable AERO completely.
Defrrag does nothing of any value on new OSs so I shouldn't bother with it. DO you have the correct MOBO drivers installed? Was it a pack or a bunch of standalone drivers (GART, Sound, Southbridge etc)? Tell us what versions you are on (and give us full hardware details while you are at it).
How much crap do you have resident at boot? Is there loads of stuff and third-party apps you have lying around in your tray? If so bin the lot and do a selective boot - this can fix any number of issues.
Let's start with that and we'll see what needs doing afterwards.
My stats:
CPU: Intel(R) Core(TM)2 Quad CPU Q9300 @2.50GHz
RAM: 4GB
System type: 64-bit Operating System
GPU: NVIDIA BeForce 9800 GTX/9800 GTX+
MOBO: abit IP35P
I'm downloading the updated driver for my GPU now
I had to update my DirectX to play COD.
MOBO drivers: well there was only ever one update back in 2008, so I was thinking of upgrading it soon, which will be another post to come.
I hate things booting up on startup so I turn it all off, just the stuff it needs.
What's AERO? I thought it was a chocolate