PowerPoint locks up when running a presentation non-stop
Nobody's entirely sure why this happens or even whether it'll happen on all computers or just some, but it's quite common. You start a looping/kiosk-mode presentation running and sooner or later, the computer locks up.
There are no known patches for the problem but workarounds include:
Using a scheduler to re-start PowerPoint and the presentation periodically
Visit MVP Tushar Mehta's site for a tutorial on how to do this with the Win98 scheduler app.
Convert your presentation to HTML and run it in a browser instead of PowerPoint or the PowerPoint Viewer