gnome session does not start anymore

[Marco Mandl]

Hello,

suddenly the gnome session does not start anymore. I can't find out what's
the problem. A few seconds after login I get an error and .xsession-error
only shows:

/etc/gdm/PreSession/Default: Registering your session with wtmp and utmp
/etc/gdm/PreSession/Default: running: /usr/X11R6/bin/sessreg -a -w /var/log/wtmp
 -u /var/run/utmp -x "/var/lib/gdm/:0.Xservers" -h "" -l ":0" "mick"
/etc/gdm/Xsession: Beginning session setup...

The Gnome Failsafe Session works but I get the following popup:

There was an error starting the GNOME Settings Daemon.
Some things, such as themes, sounds, or background settings may not work correctly.
The last error message was:
Unable to determine the address of the message bus (try 'man dbus-launch' and 'man dbus-daemon' for help)
GNOME will still try to restart the Settings Daemon next time you log in.

Please help me. I am completely lost. Already crazy thought are capturing
my mind, like switching back to Windows.

Regards,
Marco