No Video on my Gateway DX4640 Desktop Computer...HELP!!!?

Hello, I'm having an issue with my Gateway DX4640 Desktop computer. The computer turns on but theres no display. I ran several diagnostics on almost all the parts. I ordered a new motherboard, processor, memory and replaced it and it still doesnt seem to work. At this point I cant think what the issue can be. Anyone out there have an idea??? Thanks