How to edit the xorg.conf

Question

I use Ubuntu 14.04 USB boot. When I installed CUDA7.0, a black screen appeared, but I can enter console mode.

Stuff I tried:

• edit the /etc/X11/xorg.conf but it could not be edited.
• calling vim with sudo, su, su -

The results of ls are shown below:

#ls -ls 
--------------------------
-rw-r--r-- root root
--------------------------

I can't understand that. This file can't be edited by the root authority.

#lsof ｜grep xorg.conf
--------------------------
there is nothing.
--------------------------

Even in recovery mode, I was in the same situation.