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.
- use a phone charger to connect to the camera, the red light should be on.
- 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?
- while the camera is being charged, press and hold the reset button for 30 seconds. This will force the depleted battery to recover.
- turn on the camera by holding the power button.
- fully charge the camera.
You might need to repeat steps 3 and 4 a few times to force the battery recovery.