check that the 8 pin atx power on the mb is connected. also check to see if there one or two power plugs on the video card. if there two make sure both are plugged in. with the newer z77 mb that have intel ipgpu. the ipgpu does not turn off like the older intel video chipset did. to turn the onboard gpu you have to turn it off in the bios. because of this most vendors now set the intel ipgpu as the first video device. when this happens the nvidia or ati card wont show any video on it. intel your in windows and connect the video cable to it and turn the card on in windows.