Usually, this is a result of a problem with the cable connecting the
computer to the projector. Sometimes all that is required is making sure
that you tighten the plugs by pushing them in as far as they go (and
possibly screwing them in). Other times, it could be that the cable
itself is bad and needs to be replaced. It is less likely, but possible,
that there is a problem with the projector.
David M. Marcovitz
Author of _Powerful PowerPoint for Educators_
Microsoft PowerPoint MVP
Associate Professor, Loyola University Maryland
One more thing. I forgot I was responding in the Mac group so it could
be the adapter that is bad as well since that sits between your computer
and the cable. I have seen adapters that have been banged around a lot
and no longer plug in firmly to the computer.