I have a 4850 which crashes when under severe load, ie 3D mark or GTAIV. At all other times it's fine. When it crashes the LEDs on the Card go on and the computer shuts down. I think it may be my PSU as it isn't all that brilliant and I don't think the card's buggered. The +12V goes below 12V when the card is under load also. I just wanted to make sure that you all agree with my diagnosis so I dont buy a pointless new PSU.