If it is a brand new unit, check if the insulating disc has been removed prior to use.
Otherwise, follow the testing steps below
1. Remove the battery from the battery pack. Hold the battery back upside down to ensure there is nothing left inside to block the contact.
2. Install the battery with the positive button top pointing inside, observing the polarity marks on the battery pack.
3. Fully tighten the battery cap (important steps)
4. Tap the power button.
Does the small power indicator between the two switches lighten up? If so, what color is it?
Does the lower red LED light start to blink? If so, how many times does it blink before it stops?
-----------------FYI ----------------------
The power indicator (green or red, steady or flashing) shows the battery level (green is full, red is low)
The main red LED blinking shows if the light is set to the Lockout mode. (4 blinks means it is locked)
To Lock or unlock the light, press and hold down both switch buttons simultaneously for 3 seconds.