I have just finished building my new desktop, and for some reason it doesn't want to show a picture on the screen. I have a ASUS GTX770 2CU and a Samsung screen along with a LC Power 550 watt PSU. I've tried switching the cables the PSU to the graphic card, but that only shows "Please power down and connect the PCIe power cables for this graphics card). I only have one 6+2 pin cable.