Problem with Rigid R250SFA finish nailer. I cannot make the gun fire. Pressure is correct. Checked quick connect fitting and air flows through when connected. The selectable trigger is set correctly. With compressor on when I press the workpiece contact against work surface and depress the trigger nothing happens. The trigger moves freely, no pressure backing it up. Am I missing some safety lock? It's new out of the box. Is there a shipping guard I missed? Help!