If you have a Nvidia graphics card and have the Nvidia proprietary dirver installed and notice that it wont detect monitor information over DVI then try apply this:
First run nvidia-xconfig
in a terminal to generate the /etc/X11/xorg.conf
file.
Then you need to lookup your monitors specifications to find its Horizontal and Vertical refresh rates.
The edit the xorg config like so:
sudo nano /etc/X11/xorg.conf