Restart X

From

The easiest way to restart X-windows is to simultaneously press ctrl-alt-backspace. Note: this will instantly kill X-windows and any programs running within it, like your window manager and probably everything else. There will be no confirmation.

Alternately, from the command-line, type "sudo pkill X".

Alternately, from the command-line, type "/etc/init.d/gdm restart" or "/etc/init.d/xdm restart".