I played some music, heard it when playing (when touching my keyboard) but impossible to hear it afterwards (is it called “playback” ?), see the screenshot.
Perhaps is the “level” (in the drowed red circle) missing ? I don’t know how to rise it.
You’ve forced all 4 tracks to monitor their inputs (the “Entree” buttons are a solid color). They will not play back any data from disk until you change that. Simplest way is to click on those buttons.