What causes a boot to stop at Ubuntu 12.04 with the five dots? If I then do Ctrl-Alt-F1, it takes me to a login. I log in and then run sudo lightdm. Thet brings me to the correct graphical login for Ubuntu, Ubuntu-2d. After that login, system runs normally.

I got into this "mess" after I removed the Gnome desktop.

Is there a diagnostic tool that will point out the error in my ways?