Evga 8800GT SC Black screen

Evga 8800gt superclocked edition 512-P3-N802-A1

Got it yesterday from newegg and did a clean install with Vista Ultimate x64.
It works in VGA mode and safe mode but when I install the drivers and reboot, the screen goes black a few seconds after vista starts loading.
Later I installed XP and when I load the drivers for XP the screen just goes black, no reboot.

I don't know if it's an incompatibility, bad drivers, insuficient power from my PSU or a defective card but I would like to find out before I RMA it.
Drivers for xp and vista64 were both version 169.02 from Nvidia.com

Specs
Q6600@3.3Ghz stable 1.32v
4x1GB of DDR2 667@730Mhz stable 1.9v
Gigabyte p35-ds3r motherboard
Ultra 600w Psu, Max 38 amps on 2 12v rails(18a and 20a)
2x 7200Rpm sataII drives