I have the A8N-SLI Deluxe and I am wondering if it is anything to do with the drivers at all. I don't have your graphics card I have a 6600GT but I'm wondering what power supply you have, I upgraded mine to a Tagan 480watt one. Also the card, could it be faulty? Have you connected the extra connector to the motherboard for the graphics card?
If you're sure its the drivers you could try the omega drivers click here