I've had this problem before, but this is now occurring every morning. On the first boot-up of the day, the computer starts, begins showing the splash screen then suddenly changes to a black screen. This is followed by a window saying that I am running in Low Graphics Mode. The window offers 4 choices, none of which are available because the trackpad is non-functional.
Because I've been through this before http://ubuntuforums.org/showthread.php?t=2035818
I always get a message saying there is no such file.
sudo rm -v /etc/X11/xorg.conf
which brings me to a console boot-up. Then I try
which get me to a desktop. Unfortunately, about half of the time I am unable to log in as my username, but only as guest. I fix this with
sudo service lightdm --full-restart
which sometimes starts the entire cycle over.
sudo chown -R $USER:$USER $HOME
The next morning, I go through this again. Is there some way I can fix this? What information can I provide?