Playback won't play

A message gave me the option of not hearing playback when I started on a project. I took the offer. Now I can’t get it to play any more. What should I do?

The Blue button in Play mode.


Or rather, it turns Blue when you activate playback.

Thank you. As it turned out, while the blue button was on, the slide pot on the far left under “Channel” was turned all the way down. No clue how that happened.