Alternatively for a Ubuntu fix: Open a terminal and input
That will start a text-based wizard which will reconfigure your xserver. Answer any questions you can yourself. If there are questions you can't answer then go with the given default answer. If at first you don't succeed then try again. If all else fails then specify VESA as the graphics mode, which should at least give you a gui.If you have installed a video driver e.g. Nvidia or Ati it might be knocked out and need reinstalled. If you have Compiz it needs to be restarted.