Screen distorts then freezes ... help

Hi there,

I was sitting down watching a media file the other night when all of a sudden the screen became distorted and suddenly turned bright white and my pc froze. I forced it to shut down and restarted, everything was fine for a few minutes when all of a sudden the screen distorts a little and the pc freezes again.

Since then I have also noticed that when I boot up sometimes I get an error beep and the screen stays black. After a couple of attempts it will boot up normally. Also if I go into the bios it will be fine for about 20 - 30 seconds before the screen freezes, although the bios does seem to stay active in the background as I can hit 'F10' then 'Y' and the pc reboots.

I have a Corsair HX1000 watt PSU powering a 9800GX2 so I don't think the PSU is the problem. I borrowed a friends 6600GT yesterday and put this into my system and it ran for hours on end as stable as could be. As soon as I put my 9800GX2 back in the problems started happening again.

Because of this I feel I may have a faulty graphics card, any suggestions on anything else it could be or anything I could try?

thanks