If you can't turn on the camera even it is charged. There is a chance that the lithium battery is severely depleted and we have to recover this by following a few steps below.

  1. use a phone charger to connect to the camera, the red light should be on.
  2. press the reset button above the charge port with a pin (I'd recommend the pin to open phone SIM card holder). You may find the reset button in this video How to reset the camera?
  3. while the camera is being charged, press and hold the reset button for 30 seconds. This will force the depleted battery to recover.
  4. turn on the camera by holding the power button.
  5. fully charge the camera.

You might need to repeat steps 3 and 4 a few times to force the battery recovery.