I use gnome as default desktop. And I recently upgrade Ubuntu to 13.10 then upgraded gnome to 3.10. Upon restarting, it brings me to the gnome log in screen (GDM) and all I see is the top banner part so like your date, music volume, option to restart, suspend or shutdown.

Hitting control+alt+delete tells me gnome display manager will log out - it does but still nothing.

I am on the log in screen, but there is no user to select, like there normally is or was. I can boot into safe mode and drop down to shell but I am not sure what commands I would enter to get the login screen back. I am using the gnome PPA's and the "unstable" PPA, so I expected issues, but not this - ideas?