Open the xorg.conf file in your favourite text editor. This file, xorg.conf lies in the /etc/X11 folder in most standard Linux installations. Then add the following lines at the end of the xorg.conf file:
Option "DontZap" "On"
Save the file and close it. Restart your PC. And once when it is up again, you will find that you can no-more restart the display (X11 Server) using the ctrl-alt-bksp key combination. The screenshot of my xorg.conf file will give you a better picture: