Fatal server error:
Server is already active for display 0
 If this server is no longer running, remove /tmp/.X0-lock
 and start again.

(EE) FBDEV(0): FBIOPUTCMAP: Invalid argument

Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07) (prog-if 00 [VGA controller])

00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)
00:02.1 Display controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)

sudo apt-get update
sudo apt-get -d install --reinstall gdm
sudo apt-get remove --purge gdm
sudo apt-get install gdm

sudo reboot