I just performed the upgrade from Ubuntu 11.10 to Ubuntu 12.04 LTS. The updater downloaded all packages but a few ones that the system said were already installed. When asked for it, I chose to install the new maintainer's version of grub.
Now after that my system start up to the login page, some images won't load. Moreover, after I try to login, the graphical instance does not load, it just sits there showing the mouse pointer and nothing else.