Do these system boards work with onboard graphics? You may need to disable onboard graphics in the system bios, reboot, then install the graphics cards before it will work. When the machine turns on, do you hear the normal post beep? If you leave the computer on when this happens, can you press number lock or caps lock and see it light up on the keyboard? If it does light up, that means it is booting up to windows, and just not getting video. Do these cards require extra power connections beyond what the pci -express gives? If so, try different power connectors if your power supply has them in case one is faulty. Also, what kind of power supply is it that you have? Even though it may say it provides a certain wattage, not all power supplies are created equal and may not provide sufficient voltage on the different rails. I am not a power supply expert however usually cheaper power supplies like the ones that come with a cpu case are generally lower quality and may not allow power hungry devices like video cards to work correctly.