Just a quick note about how to disable the graphical user interface on your machine safely and quickly. This may be useful if you are having issues with your video card causing your system to crash. By disabling the graphics you could get command line interface to your machine.. and hopefully determine the exact problem to get your GUI to work.
mv /etc/init/gdm.conf /etc/init/gdm.disabled
This works on Ubuntu 10.04 LTS.
Remember that this would disable the graphics on all your boots. Not just the the one from which you make the change. And of course run the reverse
mv command and reboot your machine to start your graphics again.
