If everything is hooked up correctly, I would assume the problem is you are trying to run the computer off of the GPU but your bios is set to boot on integrated. If this is the case you have to boot the computer using only integrated graphics and then set boot priority to a pci-e slot within the bios. Then save, turn off, and restarted the PC connecting the GPU to the display.
EDIT: Also, is that picture of the computer as it stand right now? Where is the RAM?