Ah, didn't catch that its supposed to be factory overclocked! Definitely send it back then if dropping to 750/900 cures it. The only time my Sapphire 4870 1GB black screens is if I go over 810, still not terribly high but its performance is plenty good enough for me so I don't worry.
Untutored carnage is useless in the face of an educated bullet
The penalty for masturbation in Indonesia is decapitation