I have a radeon ATI hd 5770 that was working just fine.. The computer wasn't working so I took it off for a few months until I got a new motherboard and processor.. Now it doesn't work at all but the built in card is working so it's not the monitor.. When I turn the PC on I get a black screen even though the fan on the card itself is working.. I'm certain it's compatible with the rig I have and I've paid a lot for it so what could be the problem?