DVD picture has black square

I have a Mediamatics DVDExpress Build 5.00 on my Toshiba 4270 laptop.

Usually (not always) when playing a DVD there is this black square with four pairs of vertical lines on the screen. Usually it is plonk there in the middle of the screen - Murphy's Law! Sometimes it becomes the mouse pointer and moves around with the mouse.

I can put up with the latter, but the first is quite unacceptable. What can I do?

Terry