Xfce 4.8 on Ubuntu 12.04: Any DE choice starts Xfce. No splash screen nor Xfce session selector nor WiFi icon, no option to restart/shutdown and more

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http://askubuntu.com – Last night I closed session normally and today I found many problems: -No matter whether I try to start session on Unity, GNOME, Gnome-Classic, MATE, etc, it always start Xfce. It doesn't even show the Xfce session selector nor the splash screen. -It doesn't start the freemeteo screenlet. -Orage starts up automatically. -WiFi icon is missing (but I'm connected to the net). -On the user menu, "Suspend" and "Shutdow" are greyed out. -"Logout" is enabled, but when I click on it, it gives me the error: "The name org.xfce.SessionManager was not provided by any .service files" I don't know w (HowTos)