powerpoint viewer cannot back page to previous slide

I have a couple of PPT files in a powerpoint viewer .lst file. when the viewer is displaying the 2nd PPT file, the [page up] key does not work and cannot go back to previous slide. Is there a way to get back to the 1st slide show without having to [right-click] and select ‘go to view’ ? I am looking for a seamless way of getting around the slides in viewer by simply using [page up] and [page down], are there any alternatives ?
Thank you.