Make a backup copy of your exisitng xorg.conf:
Originally Posted by Joshgo
Open the original for editing:
sudo cp /etc/X11/xorg.conf /etc/X11/xorg_backup
Scroll down to the "Device" section. It should look something like this (NOTE: mine has been modified from the default):
sudo gedit /etc/X11/xorg.conf
Add the Dynamic Twin View line as it appears above. Now scroll down to the "Monitor" section, it should look something like this (NOTE: again, mine is modified from the default):
Identifier "Generic Video Card"
Boardname "NVIDIA GeForce 7 Series"
Option "AddARGBVisuals" "True"
Option "AddARGBGLXVisuals" "True"
Option "DynamicTwinView" "False"
Verify that the "Horizsync" and "Vertrefresh" lines are correct for your monitor. You will need to get that info from the monitor's specs, either in an owner's manual or from the manufacturer's website. Once you have made any necessary modifications, save the file, log out and restart the X server (CTRL-ALT-BKSPC).
Identifier "Generic Monitor"
Modelname "Samsung SyncMaster 753DF(X)/703DF(X)/783DF(X)/CD173A(T)"
If, for some reason, the Xserver doesn't start, reboot the PC, hit escape to get into the boot menu and select recovery. After it boots up to the command line, run this to restore the original working xorg.conf:
Then reboot the PC (CTRL-ALT-DEL).
cp /etc/X11/xorg_backup /etc/X11/xorg.conf