Hi again, today I'm almost sure it's has something to do with the sketch.
I have just tried one of our friend's backpacks, hooked it all up, the way I did the first time (when it worked) and the result is the same as before, not working.
When I comment out everything that has to do with sound instructions/functions in the sketch it works again like a clock... with power from the computer or the powerbank.
When I power it all up, I can hear a short buzzing in the speaker, as if it gets it's power.
I can only conclude it has to do with programming it all, for some to me unknown reason.
Any further suggestions how I can go on from here?