Likely Cause: The Octagon ring (combat grip) is not seated properly. Remove it to test. Install it back afterwards.
Can you follow the steps below to test the light? Most likely it shall resolve the issue right away.
1) Remove the tail cap
2) Rotate counterclockwise and remove the Octagon ring near the end of the light tube.
3) Install the battery with both positive ends facing the front
4) Make sure both the head of the light and the tail cap are fully tightened to the body tube
5) Turn on the light with the power switch on the back. Then rotate the adjustment ring in the front to see if there is any beam output.
Does the light work properly now?