how to restore default graphic driver configuration

I am running ubuntu 14 on a mac machine. recently I notice compiz was too slow, so I changed from default generic driver to propietary. after that, I got a blank screen.

I am able to enter recovery mode, and even launch the dialog to configure graphics, but it is unusable (it did not respond to keyboard nor mouse, so no way to select any option there).

I had tried many suggestions in the forum, (reinstall compiz, unity-desktop,purge nvidia drivers, reconfigure xserver-org..) but most of them seems to be for older versions of ubuntu (by example, I don't have a xorg.conf file) so I wonder if there are fresh instructions specific for ubuntu 14.

Next time you boot into Ubuntu, switch to a new TTY using ctrl+alt+F2. Log in with your username and password, then attempt to start the X server.

$ sudo startx

If it doesn't work then run this and then reboot:

$ sudo cp /etc/X11/xorg.conf.orig /etc/X11/xorg.conf

If you get an error then run

$ sudo ls -l /etc/X11/xorg.*

and copy the old xorg config file as xorg.conf

If this doesn't fix it then reply with the output you receive to the commands above. And also to:

$ sudo dpkg --list 'linux-image*'

and:

$ glxinfo -i | grep render

If you don't have dedicated graphics then:

$ sudo apt-get install xserver-xorg-video-intel

Then enter

$ sudo vi /etc/X11/xorg.conf

This command will create the file and open it for you. Insert the text below exactly as it appears and click save.

Section "Device" Identifier "Card0" Driver "intel" Option "AccelMethod" "sna" EndSection

If you have AMD graphics then follow this tutorial: http://wiki.cchtml.com/index.php/Ubuntu_Trusty_Installation_Guide#Removing_Catalyst.2Ffglrx

If you have nvidia then: http://www.linux.com/community/blogs/133-general-linux/774158-install-uninstall-nvidia-driver-33179-on-ubuntu-linuxmint