Installed a new video card and PC went blank?

I installed a new video card on my PC on the PCI 16x1 slot to hook it up to the TV, but it want turn on. There is power, just that the screen stays blank. I tried two different video cards and it does the same thing. Its a 512MB video card with 256MB min.requirements and the PC has 512MB.|||Try switching video input devices... when you install a new video card it may be that your computer still thinks the cable is hooked into the on-board video.|||Check your BIOS settings to ensure the PCIe slot is selected as the video source. You may have to connect to your old video setup in order to do this.|||Check your Motherboard manual, there may be a BIOS setting to disable the Onboard Video and or a Jumper Setting on the Motherboard.