In case your headphones is not turning on when you press the power button (no light) :
1. Make sure your battery is charged
2. If you're certain that your battery is charged, your headphones are probably stuck and need to be rescued/reset.
Try to put it in "Rescue Mode"
In case your headphones are still malfunctioning, please reach our support team by creating a ticket on the Help Center or by email at firstname.lastname@example.org.