If your laser isn't turning on, there are a few things to check. First, the isolator strip must be removed from the battery housing before the laser will turn on. Unscrew the front of the laser and remove the little white piece in between the batteries. Second, the batteries must all be facing in the same direction and all must be facing in the correct direction. If you are unsure which direction, try both! If that still did not work, the batteries are likely dead and need to be replaced.