4850 freezing & black screen help

Hello,

I just brought a Visiontek 4850 card to install on my Q6600 (oc 3.33 ghz) and Asus P5Q Pro board, 4gb pc6400. I am experiencing computer freeze and black out while in vista 64 bit.

First off, before the upgrade, I was using ATI Powercolor 3870 card on this same system and ran smooth with no freezing during normal or gaming use.

Is my new 4850 board defective? I am using the latest catalyst 8.10. I have the fan turned to 60% and idle temp for the card is around 50C. I am using the mfg default setting.

Thanks