Mossy has a limp trigger

[SPIKE FSU]

So my father in law gave me a Mossberg 835 12 gauge, and said if I can fix it I can have it. It doesn't seem to be too old. I'm guessing around ten years. It needs a good cleaning. The problem is the trigger isnt doing anything. I can cock it, and pull the trigger, but nothing happens. No clicking, and it only moves about a millimeter. Could this be the firing pin, or any of its components? Or should I start with the trigger assembly?

 

[MuleShoe]

Pull trigger assembly see it there's any signs of rust. 835 trigger . Last one I had like that had been dropped in water and left to air dry. Some of the metal parts were rusted and stuck. They are simple to work on.