Wind up clock problem....?

My grandpa gave me his old antique Montgomery Ward 31 day wind up clock. Since trying to put it up in my home it will not work. The running joke is that it was on their wall so long it won't work on my wall. It is fully wound up and cannot turn the key anymore. So is it a mechanism problem or a pendulum problem. It will work for about 3-4 minutes before the pendulum stops. It still chimes when ever I move the hands. Is it something I can fix or should I get it looked at by a pro. Don't want to waste money if it's just something I can move with the pendulum. Thanks