Oooo...this could be bad. First of all, make sure a moltex connector is plugged into the card - some cards, especially the 6800, require extra power directly from the PSU.
If then it doesn't start up, try an old card, and if that works, It probably is the card.
AMD Newcastle skt 754 3000+
Elitegroup 755-A2 ATX motherboard
512 DDR RAM
120 gig PATA Hard drive
128 mb AGP 8x ATI Radeon 9250
300 watt 12 volt psu
Antec SLK 1600 case