Gnome Shell only works when using external monitor
I have an Toshiba Tecra R950 with F17 x86_64. At work I have it connected to an exteranl LCD monitor trhough the Display Port and I have NO problem with this configuration (dual monitor, closing the laptop and using only the external etc.). I also connect it to a USB keyboard and mouse.
This laptop comes with a Radeon HD 7570M and I am using the Xorg radeon driver.
Ironically, when I boot without external monitor (using just the LCD/LED screen) the GNOME Shell crashes on login with the "Something have went wrong" message. I do not see any relevant message either in syslog or Xorg.0.log
Other environments (like Cinnamon and LXDE) work properly in both environments.
Could anybody help me, please? Where should I look for information? Which files/logs should I look for?