#1 Simple Try(1)Please try different brandbatteries of CR2032 3.0V. Because some customers made the feedback that theirred dots did not turn on when they put new battery inside, but the red dot turn on normally after they put different brand battery inside. (2) Please pull the metal contact.#2 Little complex tryStep 1 : Relax the screw.Step 2 : Put battery directly on the metal contact “+” and “-”.Step 3 : Look Through the red dot / Take a photo. Step 4 : Assemble ! Make sure the “·”+“0”+“|” at the same line.If the method above can't help you, please contact us directly by<retail@vectoreoptics.com