Fix failed to start session in Ubuntu

 

  When you are at login, press Ctrl+Alt+F1. It will take you to command line interface from the GUI. In here, type your username and password. Now, you can try the following command to install Unity Desktop:

sudo apt-get install ubuntu-desktop

sudo apt-get install --reinstall ubuntu-desktop

sudo reboot 

转自：http://www.cnblogs.com/xiaojikuaipao/p/5770453.html