What you can do is have it loop continuously until you press Esc.
To do this:
1- Open the powerpoint presentation.
2- Click slide show --> Setup Show.
3- Choose "Browsed At A Kiosk". (So that it does not respond to mouse clicks).
4- Choose "Loop Continuously Until Esc".

Remember that for point 3 to work you need to do the following first:

1-Slide Show --> Slide Transition.
2-Advance slide automatically after (Put the number of seconds you want each slide to stay on the screen for).
3-Click apply to all slides.