Vista - Windows Vista Ultimate x64 crashes!

Hello,
i am using windows vista ultimate x64, and in random times when i am playing some games like worldd of warcraft, oblivion, PES 2009 etc. the computer freezes and the screen becomes full of squares of the last image i saw before the computer crashed (like: if i was casting a spell in world of warcraft i would see that very screen but with little squares, can't really describe it as it's weird). I tried re-installing video drivers and i made sure they are for x64 vista version. My computer spec is:

Graphics Card: ATI RV770 [Radeon HD 4870]
Audio: Sound Blaster X-Fi Platinum
CPU: Intel(R) Core(TM)2 Duo CPU E8600 @ 3.33GHz
Motherboard: ASUS P5Q DELUXE
RAM: 4GB (2x2GB) DIMM DDR Synchronous 800 MHz (1.2 ns)

Any ideas?
Thanks

I am having a similar problem when I play Bioshock and Crysis. Pixels just pop up all over the screen as it freezes. I have Vista Business x64, but I have NVidia card.
I hope we can both find a solution..lol

A lot of times its a sound issue, believe it or not. You should try configuring your default output. Like COD5 either won't run or runs terrible in vista unless you have your default output set to 44100hz.

Its artifacting and its usually down to your card overheating or faulty GPU ram , i know this might sound odd but try underclocking your gpu ram just by 5 or 10 mhz and see what happens.

(im assuming you tried the usual , latest drivers for GPU/Chipset etc)

Hey thanks for the replies!
I am currently trying to test the sound suggested by vistaHater9000.

%archie123:
I don't know how to underclock my gpu ram. Can you help me out a bit? Btw, yes i have updated all drivers.

You can download RivaTuner 2.2. I think it works with ATI video cards. I use it for my NVidia card. You can use this guide to help you out. It shows how to adjust fan speeds, but you will get the idea after reading it.
Vaguetech - Rivatuner v2.07-11 Guide

Okay, i reduced GPU Memory (hopefully that's what it was) from 900MHz to 880MHz and still nothing. I tried changing sound to 44.1KHz as well, no luck! Freezes again. I even increased the fan speed but still nothing.

Bump

If you guys are getting freezes then usually Ram is the problem. You have Ram settings that aren't stable or if your system was once stable and began to randomly freeze up then you have Ram that is failing.

If it only happens when the system is hot then your GPU may be overheating.

So should i remove one of the sticks or change the settings in the bios?