I had this problem when I first got my pair as well. First of all, make sure the headphones are charged and that you are using the charger that came with the headphones if you are charging it for the first time. Then to fix the problem hold the power button (left side above slider) and the volume up button (top-right) at the same time for about 10 seconds, this will shut down the headphones completely without the voice saying “power off”. Then turn them back on and while listening to something, start moving the bass slider up and down and it should work again after a couple seconds