Power does not turn on / power is turning off automatically
Power does not turn on.
When the rechargeable battery has no power remaining, connect the headphones to an AC adapter or computer using the supplied USB cable to charge the battery. link
Power is turning off automatically.
The auto standby function has turned on. In auto standby mode, the headphones automatically turn off after no operations are performed or they are stationary (when they have been placed on a surface such as a desk and are completely motionless) for at least 10 minutes. To turn off auto standby mode, slide the NC MODE switch to the left and hold for approximately 5 seconds while auto standby mode is on. link