GTX 280? Freezing my game PLEASE HELP

HELP ME PLEASE !


I currently have just had someone build me a computer with these specs:

PSU: 850watts
GPU: XFX GTX 280
MOBO: Asus Striker II NSE
CASE: Antec Gaming Case

Now i'm not an idiot at computers but i just suck at this "building a computer thing". So please help me...

Everytime i play a game or 3d application, my computer suddenly locks up/freezes/crashes. There's a video on youtube showing you but i cant find the link. The audio/sound loops over and over fast. There's nothing i can do including ALT CRT DEL, or switch to desktop or QUIT. The computer totally freezes.

It first started on assassins creed my first game on here, but it only happened every like 1hr or so. Now it has become frustrating more with me playing bioshock and it happening every 5 - 30mins. Its got damn annoying.

I have all updates for VISTA, i also have updated BIOS, GRAPHIC CARD, and MOTHERBOARD and AUDIO.

I also have a program on here called: AI SUITE
I know its for overclocking and stuff (im not one that knows much about overclocking, but when something says it makes the computer faster i press it), but whenever i choose a option of 3-in-1 Overclocking it does it, and then when im doing something 30 secs later it locks up/freezes the computer.

Also another thing my system doesnt seem hot either, the temperatures of the computer are fine.

And i have 4 x 1gb RAM. running on Windows VISTA 64bit.

My graphic card does not have an amber colour LED on the back (its green) when this happens aswell (ingame/out of game).

Any help would be appreciated. There's many instances of this on the web, but mine is a bit different. Please someone help.