Which display port are you using, the graphics card output, or the motherboard output? Try the other, sometimes one just doesn't work for some reason. If you're using the motherboard, obviously you're using the wrong video output, but if you're using the GPU, there could just be some error, and the video may still work from the Motherboard output.
Next I would try unplugging and plugging in all of your power connections, to make sure that nothing is miss-seated.
Otherwise, you could look up the combination of colors, or the lighting patterns, of the debug LEDs (either online or in your motherboard manual), and see if you can figure out what error your motherboard is try to tell you.