Greyish screen with stripes

I bought an hp pavilion pc that came with windows 7 64bit with amd M880g with ati mobility radeon hd 4200 installed on it... i installed WoW and played it for several months with no probs then it started freezing up after about 5-10mins of game play first it started with a black screen and would have to use the power button because nothing else would work would b completely locked up. now same prob only with a like greyish screen with stripes.

i have tried reinstalling the game.. that didnt work, i did a system restore and turned off updates to c if maybe it was a recent update that caused it and still same prob which is weird since it worked like that for a couple months before getting the prob, o and i didnt install anything like drivers or nothing just as is, tried running in compatibility mode and still same thing, tried reformatting the hdd and installing windows 7 ultimate (borrowed from friend since he can play just fine) didnt work, so tried again to do a clean install and use my factory restore again hoping i missed something but still same thing, installed speedfan to check for overheating and it was fine that wasnt the prob, tried putting all the settings on the game to lowest and did the same thing.. im at my wits end i really dont want to have to get vista on my new pc and it seems really weird to me that i was able to play it for several months with updates turned on.. o and i made sure that all my drivers were up to date.

if u can pls help me i would greatly appreciate it!!!

thanks