My JBL Flip 4 was working fine one afternoon..The light which displays the remaining battery stayed on even if the speaker was turned off..later it stopped emitting any sound even though it connected to my phone very easily (via Bluetooth,or even AUX).I tried everything like resetting the speaker by pressing the 'Volume Up' and 'Play' buttons together. After all the annoying problems I just pressed the power button for around 10-15 seconds while the speaker was on and it turned off. Later I just tried turning the power on and voila!The sound was back!Try it out..