I don't know how to take a screen shot at the moment you're logging in, so I'll try to explain the component I'm referring to.
If you set your Ubuntu to ask for password before the system start, of course you will be able to choose a user, if this user is selected you can type the password and then click on symbol that looks like ">" or pressing the Enter key, after that this symbol will disappear and a infinity progress circle will replace it, this circle should flow/circulate.
That's the problem, in my version of Ubuntu, 13.04, it doesn't happens, it looks frozen. Also I remember to have the same problem with 12.10, but when I switched to 13.04 I did a clean install (removing the older version first).
Do someone else have the same problem? Do is possible to fix it?