The bios may have defaulted to onboard video out so you need to attach the video cable to the onboard video out. Usually, the VGA is default but I'm not too sure with these later model motherboards. Once you do get video out display, you need to change the display mode to the video card (could be called PEG1).
I sounded like a great solution but i tried to connect 2 different screens to the onboard VGA, DVI and HDMI. But no success, still no signal