Hi, viajera. What model is your laptop? Assuming it's a Powerbook G4 of some sort, this article will help you identify it precisely:
http://support.apple.com/kb/HT3065
I don't know of any kind of software problem that can cause what you describe, so I'm sure there is a hardware failure of some kind. Is the blank white display affected at all when you change its tilt angle? If what you see on the display changes even momentarily when you move it — whether or not a proper display image ever appears — you can be fairly confident that the video cable is damaged where it passes through the display hinge. If the machine has ever been dropped, and the hinge or the back of the case is visibly deformed in any way, this is almost certainly the problem.
It's also possible that the video cable is not securely connected inside the Powerbook's case or inside the display assembly. Where the connections are and how to access them varies a great deal from one Powerbook model to another, so knowing which one you have may be very helpful.