I found out after much research that this is a common problem with XFX HD 4850's, so I've sent it off to scan, will have to wait and see what they say, though it's going to take them an extra 10 days because they send it off to xfx or something...
... because the problem has been there since the start, is it possible to reclaim the returns postage do you think? :s
It did cost me over £6...