Powerpoint audio not working

I am a student and my professor posts weekly powerpoints with voiceover. When I download the Powerpoint on my mac, the slides show up but the audio does not. When I download the Powerpoint on my mom's Dell, both the slides and the audio work. Why does the audio not work when downloaded to my Mac? I also tried using Keynote - same situation. The slides appear but the audio does not work. Please advise.