"Repair the GUI System
One of the most common problems in Linux is a broken GUI configuration. The X Windowing System (Xorg) is the most common GUI system in use on Linux systems today. Unlike the Windows GUI, (which is practically inextricable from the rest of the operating system) Xorg is simply a program that runs on top of the base Linux system. Because of this, it can be easily repaired.
"The X Windowing System uses a file called xorg.conf to maintain the GUI configuration. It contains information about your graphics hardware, the driver it uses, (in the case of NVIDIA or ATI devices) your available screen resolutions, and even settings for your input devices. The best way to avoid any problem is prevention, so you should always have at least one backup copy of important files like xorg.conf and be sure to save a copy of the current working version each you make any modifications to it.
"Don't panic if the worst happens and you find yourself without a working xorg.conf. The base system is probably still operational and it is possible to carry on without the GUI, although some distros might complain a bit if Xorg refuses to start. Many modern distros (like Mandriva, Ubuntu, and others) have a safe mode or recovery mode that provides a root-level command prompt. From there, you have access to the bash-friendly utilities and tools that are essential to fix your system. Even better than that, your distro probably has a special tool which can repair or completely regenerate xorg.conf."
