No sound in the presentations on Saturn

Hi guys!

Finally, I have time to watch some of the presentations on Saturn and I tried to do it now. Unfortunately, I cannot hear the sound of the videos but only read the subtitles that are constantly changing. What’s the problem? I have several programmes that can play videos: Groove music (the sound of this programme is turned off so I don’t know how to turn it on), VLC media player, Winamp.
Could you please help me? Maybe the problem is with this programme Groove music?
I would be grateful for your answers.