I didn't overclock it or touch it in anyway from when it was installed. It worked fine for first 2 weeks with all games.
Its Sapphire HD5870 2GB GDDR5
The temp is fine, no over heating.
Things have gone from bad to worse with it over the last 24 hours, pixels are appearing more and more and occasionally the screen goes white and windows gives a graphics card error message saying it recovered. This happens even when just looking at a photo.
I have arranged to get a replacement card this week from the store.
Thanks for all your help anyways, just seems like a faulty card.