Cheat Engine

[NothingToShow]

So here's the story:
I used to be a happy boy with an average computer which were able to play all Steam games just fine, but all of a sudden I wanted to improve my computer, so I bought a new graphic card (Zotac GeForce 8800GT) and a new motherboard (Asus P5K Pro). After the new hardware was installed and so on, a few of my Steam games started to crash/freeze while playing, so now I'm a sad boy.

It works just fine with CS:S, Half-Life 2 (Normal, EP1 & EP2), but for some reason, it doesn't work with Team Fortress 2 and Synergy, the Half-Life coop mod, and most likely a lot others which I haven't dared testing. I start the game, join a server, and plays for random amount of time, and suddenly it freezes, and the sound keeps looping, I can't do anything, but to restart my computer.
I've updated all my drivers, but no sucess.

Any ideas? (I've read somewhere that Anti-Virus' might crash the game, but can anybody confirm it?)

(If anything in this topic sounds stupid, it's because I suck at hardware stuff)

[Nick :3]

Have you tried reinstalling the games that crash?

[NothingToShow]