usually you have to have the card in a specific slot for single operation. READ THE MANUAL for the motherboard; make sure you have the vidcard in the correct slot and all power connections are .. connected.
Otherwise it could be a just about anything, bad powersupply, motherboard, videocard
It should attempt to boot, even without a hardrive or RAM, am I correct about the RAM>?
Sounds like a first boot Strangestranger, no OS...