Could you explain your problem in more detail? What kind of computer are you running, what version of Ubuntu, and what is the exact problem?
Display problems are pretty common after a fresh install of Ubuntu; especially pre-Gusty Gibbon. Are you running 7.04 or 7.10?
Also, what architecture are you running? Intel or PPC? Ubuntu can be pretty flaky in its PPC incarnations.
To fix the problem you're probably going to have to reconfigure your xorg.conf file, either manually or automatically. To answer your question in more detail, however, you're going to need to fill us in a bit more.