First easy try (but that will probably not help), try reconfiguring Xorg: $ sudo dpkg-reconfigure xserver-xorg
If it does not help, you can try to create a file /etc/X11/xorg.conf with a "Screen" section and "Display" subsection(s) where the authorized resolutions are listed. I do not have the time to give the details right now. However, you will easily find examples on the Web (like this one). Be careful with the refresh frequencies. You can damage the monitor by forcing them to be out of range. In other words, you had better start by finding the technical specifications of the monitor.
