Please follow the steps below to test the light
1. For testing purpose, remove the tail cap first then unscrew and remove the Octagon ring from the end of the light tube (important step)
2. Install the battery with its button head towards the front of the light
3. Reinstall the tail cap and make sure it is fully tightened.
4. Test the light again.
5. If there is no light, connect the USB cable and charge the light for a few hours. Test the light again.
If the light works now, you can reinstall the Octagon ring back to the light. Make sure it is fully screwed to the end or it will prevent the tail cap from tightening.