See the discussion on this board titled "Contender won't fire" sounds like you had a sticky interlock. Mine did the exact same thing, but I had to use a little cleaner to unstick it. sounds like yours loosened itself up after being opened and closed a few times. I'd get some spray cleaner (lots on the market, and although I'll probably get some strong reaction to this, I use carb&choke cleaner) flood the whole thing to really clean it up, then use a dry lubricant.
Helicopter Bill