The ubuntu session uses compiz as the window manager.
Originally Posted by Thechromester420
The unity interface is a plugin for compiz.
The Unity plugin may be disabled.
If you have no way to open a terminal, right click on the desktop and select new folder.
Click on the created folder to open the file browser.
Navigate to /usr/share/applications and click on "Terminal"
In the terminal run ...
This will set unity back to defaults.
dconf reset -f /org/compiz/
You could now run setsid unity to reload unity/compiz but on occasions I find it does not reload properly
and you may need to do a hard reboot,
so it may be safer to log out.....
Log back in to see if unity now shows.
If not, you may want to install the gnome flashback session while you try and fix the ubuntu session.
This will give you a gnome-flashback and a gnome-flashback (no effects) session
sudo apt-get install gnome-panel
to choose from at the login screen.
Use the gnome-flashback (no effects) session as it uses Metacity and not Compiz as the window manager.