ok i get this progblem every 4-5 month..
I ussally get the problem when i play a video game...
the grafics in games is getting messed up...and it effects the hole comuter - videos are coverd with spots, even the booting progress is messed up...here ill show you some examples:
booting:

its not a camera problem, thats how i see the screen...:

in game (Counter Strike Source):
BSplayer: (BTW videos working just fine with Virtualdub)
Desktop:
Usally the problem is getting fixed by itself with time or i could fix it with really overloading the computer with tons of games working togather at once and i kept it for like an hour or 2 - that would ussally fix it
I used to have this computer
Amd Athlon 1700+
512 ram 133mgz
some gigabyte motherboard
ATI 9600xt
and a 400w suppoeter
now i bought new parts:
Intel Core 2 Duo E4300
asrock dual seires
starex ddr 2 667 1gb
i still got the same Video card and power supporter...
Now i cant overload the computer becuse its much better so the overloading method isnt working ;\
I got the problem last week and i cant fix it...
if anyone got any idea what could be the problem and how i could fix it...please try to help...Thanks ! ;]