Frustrated Beyond Belief

I've been building computers for a few years now and have never had this problem. I built a relatively nice machine with an AMD CPU and NVidia 6800 LE video card. The machine runs fine except when I try playing certain games. I installed World of Warcraft, and upon the game loading the freezes and the sound stutters. I cannot CTRL-ALT-DELETE it, I have to manually reset the machine. I updated the drivers on all my hardware, ensured Windows was up to date and ensure Direct X 9c was installed. Still no dice. I then tried America's Army and it freezes after about 10 seconds doing the same thing. Guild Wars let me log in and start playing, but then it too froze. Thinking it was overheating, I installed some third party temp monitors. The highest my VGA card got was 65C which isn't too hot. Then I downloaded and installed the Doom 3 demo. IT PLAYED FINE the entire time! So it seems to be an online game issue. Any ideas?

 

Did you install your drivers correctly? IE: Uninstall old set, reboot, reinstall new set, reboot. Also what about mobo drivers and BIOS updates?

 

Well, I reformatted and reinstalled windows with the drivers. installed ONLY America's Army as far as 3rd party software, and it freezes within 10 seconds. Tried other games, even Sacred froze. Went out and bought a new graphics card (ATI x700) just to see and it does the same thing. What could be causing this? I am trying a new Ethernet card and processor tonight. If that doesn't do it, I am RMA'ing my MSI K8 NEO mobo. Has anyone else had this kind of problem? I even deleted Punk buster!