Password prompt never shows up on login screen

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http://forums.fedoraforum.org – I've got Fedora 18 with Gnome. When I click a user name on the login screen, the other ones disappear but the password prompt never shows up. It stays this way for a few seconds, then comes back to the original state with the list of users. So I just can't login... I clicked on "User not listed", and typed in my username, but then pressing Enter or clicking on the "ok" button does not do anything either. It just stays on the username prompt. I was able to login on a command line terminal with Ctrl+Alt+F2, updated the system, rebooted, but the problem still exists.. (HowTos)