HOW TO REMOVE XDM FROM LIVE CD.

What i know to remove xdm (when it's fail) using this command:

Code:
# update-rc.d -f xdm remove
but the problem is, in recovery menu I can not select netroot option (see my thread http://ubuntuforums.org/showthread.php?t=1553370 )

either I find the solution for that problem (for the future, i need recovery mode also) or remove xdm by using live cd and install gdm again.

Perhaps my problem start because i do combination of this in the same session

first, I remove the splash screen form
Code:
gedit/etc/default/grub
then i change the file
Code:
/etc/gdm/custom.conf
to enable xdmcp from this thread http://ubuntuforums.org/showthread.php?t=1471703, then i installed nxserver. the result: fatal!

the only one left that I can not fix is remove the xdm (because in recovery mode/menu i can not select netroot)

pls help