One of the major problems with audio in a PowerPoint presentation is that the audio is not embedded in the slide show.
Consequently, it plays on the machine it was created on as the Audio file is also on that machine, but when it is moved to another machine, the audio fails to play because PP cannot find the audio file.
This could be the problem with your PP shows. Have you checked the audio on a Windows machine?
Do you know of a program that will allow my Mac (Snow Leopard) to play the music included with most Windows PPS slide shows. Keynote (a Mac program) displays the slide shows perfectly but I can never get the Music.