Hi, I am having this problem sometimes too and am still figuring out what I am doing to get it working, I always seem to get there eventually. One of the things I have discovered is to make sure that you are in proper octave range of the instrument that you are using, I change the octave setting on my small midi keyboard to test this problem as it happens quite a bit for me. I also am making sure that I get the keyboard on the virtual instrument to produce a sound before I try anything else, like using the midi keyboard and such. I will try to keep track of exactly what I am doing more often, someone else here probably knows a lot more than I do since I am just starting with MM, but that is one idea to get started. Sometimes I have set the focus on the object, or reset the instrument track, or hit the play button and seemed to have brought things to life as well. Another problem I am having is that the MM instruments sometimes seem to have the volume set to zero or it resets to zero when whenever I replay the track, even after setting it to a higher volume - this is of course a bit frustrating. Investigating the event controller and program change (PC) commands for now. That is still a tricky one for me to understand what causes the volume setting on an instrument to stay put or to hold a change.. Best regards-