Was working fine until today, but now during the lessons when I press play on the videos, it plays the video but no sound comes out. Please advise on what to do.
What version are you using (web, iBooks, iOS, Android)? You might try rebooting your device to see if maybe you ran out of memory or something.
Dave
Same thing happening here. On iOS 9.3.5. Reboot did 't work… Videos play, just no audio.
Are you using the web version or a version from one of the app stores?
Also can you check your mute switch?
Dave
sound doesn’t work what do i do?every time i play a song it doesn’t work then the sound stops, and the videos stop working.
Also when I compose, it does get plotted,but no sound comes.very frustrating.Please help 
I’m having the same issue. It was working fine on y windows computer in my chrome browser, then all of a sudden the play buttons are greyed out and when I click play, the video and audio refuses to start.
which browser and OS/device type are you on? That sounds like a plugin or memory error. Can you try restarting to see if that fixes the problem?
Dave
Same here. Both Hooktheory one and two the sound doesn’t work. On iOS latest version (but also the one before as well)
Did a deeper search. Fixed. (Oh so simple too, nice one) thanks! Sound not working / no audio on iOS app (iPhone, iPad) [Fixed]