We'll need a little more detail. What version of PowerPoint and/or the
Viewer do you have? How have you been trying to start them? What happens
when you try to start them? Have you installed the latest service packs for
PowerPoint? Are these presentations you made or you got from someone else?
What version were the made in? Have you been able to start these and/or
other presentations in the past? If so, what has changed since this stopped
working?
--David