I use Ubuntu 12.04. I recently tried to install gnome-shell-extensions-commons. After that I powered down my laptop. Now when I try to login to gnome-shell the menu and top panel do not show. I am not sure whether gnome-shell-extensions-commons is the one responsible for this.
Update : I tried to purge and re-install gnome-shell but still no change. Gnome-shell just doesn't load up. Also did autoremove before installing.