[Howto] Restore your previous xorg.conf file http://ubuntuforums.org/showthread.php?t=258186
http://ubuntuforums.org/showthread.php?s=9784daef1bcbee2e227146c0a1bdc08b&t=1421623&page=3
Uninstall NVIDIA drivers http://ubuntuforums.org/showthread.php?t=1046504
Troubleshooting X lockups: https://wiki.kubuntu.org/X/Troubleshooting/Freeze
Restore default x.org:
sudo dpkg-reconfigure -phigh xserver-xorg
nvidia-settings -q NvidiaDriverVersion sudo update-alternatives --config gl_conf
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