laptop’s screeen goes black and hangs

My laptops (XP) screen goes black and hangs at random. Specially when I hit the monitor tab in display properties, advanced. If I boot linux on the same laptop but with an extra screen then the main screen remains black but the extra screen works normally, no hangs!
In XP the second screen remains illuminated but the system hangs.
I would appreciate if one can guess where to look for a fault, is the monitor faulty or the driver?
Dimitris