DELL XPS not reverting to onboard screen from DisplayPort

I have a Dell XPS 13 and I have it connected to a DisplayPort to VGA and once I disconnect the laptop from the displayport the screen on the laptop does not revert to the Windows Screen. You can tell that the screen is on but you can't see nothing on the screen. But once you connect the displayport back you can then see the screen. I tried to duplicate the screens that didnt work and I even tried to extend the screens, that did not work as well. I have tried different display ports from displayport to vga, hdmi and dvi, none works.