MPEG clips are not visible through projector

[mal]

I have created a presentation on XP using clips via MPEG
format. These play fine on my laptop, but when I plug in a
projector, the rest of the presentation is fine, but it is
hit and miss as to whether the MPEGs are visible.
Invariably all I can see is a black screen.

When I burn to CD and play on other machines, I have the
same unpredictability.

Any ideas.

 

[Sonia]

See:

How do I hook up this video projector?
http://www.rdpslides.com/pptfaq/FAQ00370.htm

Videos play correctly on computer but not on projector (black box)
http://www.rdpslides.com/pptfaq/FAQ00467.htm