Enter in root terminal:
$ sudo dpkg-reconfigure -phigh xserver-xorg

Select your video card by scroll up or down keys on your keyboard) and then hit enter.
the next select the resolutions that you would like to be available for Ubuntu by using the arrow keys to scroll up and down, and the Space Bar to select them.

Restart X by clicking Control+Alt+Delete (backspace). to set up new resolutions.

This starts the Xorg config process.

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf_backup
sudo dpkg-reconfigure xserver-xorg
sudo xinit — :2

Look for errors:

tail -f /var/log/Xorg.0.log

Restart all servers by bouncing XDM (or gdm or kdm):

sudo /etc/init.d/xdm start

This starts a new X server — usually on tty8 or tty9 (CTRL-ALT-F8). You can go back to the original X server by pressing CTRL-ALT-F7.