The only reason I can think of to plug a cable from motherboard to graphics card is for audio that comes through to your graphics card's HDMI out plug. I'd disconnect this cable.
Do you have 2 sticks of RAM? If so, try just using 1 in the slot closest to the CPU. If this doesn't work try the other stick. Try it in the slot furthest from the CPU also.
Check the Asus website to be sure that motherboard supports the latest 45nm quads without a BIOS update. If it needs a BIOS update first, you'll need a compatible CPU to do the update, which is a PITA .
Let us know how you get on.