Laptop display shows nothing after vga-projector is being connected

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http://askubuntu.com – after plug in my external projector to the vga-port my laptop display becomes black. Only the external projector can be used. The system-settings doesn't affect it either. I'm using a integrated graphics card from Intel (INTEL GMA45). This problem is present since updating Ubuntu to version 12.10. Before that everything went fine (cloning, extending displays). Are there any occurences regarding to updated software (e.g. Xorg) ? Kind regards (HowTos)