Did you unplug the video card while the PSU was off? you probably did. Did you plug the VGA, HDMI, ot whatever cable you use for integrated graphics before turning the system on?
If you did all this, and still no display. The problem is that the mobo BIOS is not detecting the change of hardware and is trying to display an image from the dedicated GPU. This has happened to me before. The best way to fix it is going into the BIOS and selecting display hardware as the integrated Intel graphics. To do this you would obviously have to plug your video card back and then do this. If you don;'t know how to do this, or for any reason you cant, you can turn off the computer and turn it back on hoping that the mobo would detect the change...