So i presume the power cable is plugged in...
What a bummer...This is if you're really desprate - try finding like a fry's or summat w/ a good return policy - buy a card, plug it in, make sure it works, then put back into the box and return it.
Or try getting a new card from where ever you got it...
Hold on, are building this computer? Was the computer working before you put the 6800 in? Cauze it might not be the grahpics card, it might be something else...
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