This question already has an answer here:
I have two computers. One intel i3 core with nvidia graphics card and the other amd 4000+ with nvidia graphics. In both these computers I upgraded from 13.10 to 14.04. Now both these computers are stuck up with the chosen wallpaper showing ubuntu 14.04 lts and nothing else. right click, ctrl+alt+t does not work. but ctrl + alt + f1 works and I am presented with terminal prompt. I have already updated nvidia drivers. tried reinstalling unity and desktop but no effect. I even tried sudo dconf reset -f /org/comiz/ but the outcome was Unable to launch D-Bus without X11 $Display.