Computer help forum: real problem with pc, seems graphics related

Hi iv had my computer for a couple of years now. The spec is:
OS: Windows XP Home SP3
Graphics card: Nvidia Gforce 6800 GTX
Sound card: Auzentech prelude
Motherboard: Asus P5N32E-SLI PLUS

The problem
This morning I turned the pc on and left it. When i came back my 1st monitor had a blank, black screen. My second monitor was flickering with a very wierd pattern, 6 horizontal stripes across it, i cant remember what colour but i remember purple being in there, kind of like something ud expect from an old games console like a zx spectrum when loading a game or something.

I turned it off and on, there where a few lines down the 'AI lifestyle' logo that shouldnt be there, i got into safemode which worked fine, i did however get a strange flash for a few seconds when i went into control pannel.

I didnt rly know what to do, so i tryed loading windows normally again, everything went as normal even the Logo was clear again, and i was in windows, loaded up a webpage, must have been about 20 seconds in before a few dots displayed next to my cursor and followed it as i moved the mouse, and there were purple blotches all over both screens, flickering(more apearing then disapearing). The cursor dots increased as i moved the mouse around, it looked like a little chart eventually.
It wouldnt let me click anything but i could move the mouse around. I pressed control+alt+del, it took a while but the menu apeared but the buttons/tabs/menu was blank just the boarders where displayed. My pc seemed to slow down a lot which makes me wonder if its not just my graphics card, since i would expect just the colours to go rather than the normal running of the pc.

Backgroud:
Yestarday i was playing a game called call of duty4 and all of a sudden the colours got really screwed up, and everything froze, i believe i could still hear sounds of the game continuing, people shooting ect..(it was online so there where other people playing) but my memory is kind of faded on this event so i could be wrong. My second monitor displays the wallpaper and there where purple blotches all over it. Through hitting various key combinations, esc+ctrl, ctrl+alt+del ect... i managed to get out of the game and close the game down from the processes menu. I thought nothing of it and watched a tv program on the pc.

Later on, i decided to play again, so i was playing for about 10 minutes then the same problem occured, this time with a different pattern but purple blotches on the wallpaper on my 2nd monitor again. i couldnt get out this time to close it so i turned the pc off. Started it up again and did a few other things then turned it off and went to bed.

Thanks for taking the time to read my problem, and any help/advice would be very much appreciated.