Replying to Severe computer problem, Help Me please!

hey my computer just started to act up a few hours ago

the problem is that the screen is all sorts of different colors and isnt displaying properly, its not the moniter, ive checked hat by trying one from a different computer

windows still loads fine, its just the display thats all scrwed up, some time it will put random charactors on the screen, sin a random scattered pattern, the colors occasionally switch around, and once and a while the screen works normal up until a certain point and then the problems start

i first noticed this playing a game when after a while playing it would do this, and id have to reboot

now its doing it pretty much all the time, even in the POST  and the BIOS screens

i have a Geforce 8500 GT graphics card and an AMD Athlon 64 dual core processor on a mach speed MSNV-939 board

could it be that i overheated something? a BIOS virus?

any good help is appreciated and gets ++++K