Not responding to the bit

Question
I have an 18yr old Tennessee walking horse. I got him in December 07. The people before me rode him about a year then left him to pasture for 3yrs. The people whom owned him before that, would "ride him into town". He is rode western but reins  English. My problem is, he won't walk. He always wants to run and getting him to walk is always a fight. Not to mention that he has no gaits.He wont trot because he'll try to run. We've tried snaffle, walking bit, and getting ready to switch to a hacking bit I think its called, with a nose band. I've tried pulling gently all the way to full force, and he will not respond to it. The guy who owns the stable thinks he may have been run a lot and also developed a hard mouth.Is there anything i can do to get him to respond? or a way to retrain him on the bit?

Answer
Hi Mandie, you seems as though you might be a bit new to the Tennessee Walking Horse breed.  I apologize if my observations are incorrect.  I haven't a large amount of experience with this breed, however my father was interested in buying one once.  As a result I was able to ride a few during the selection process.  Walkers have three gaits: flat walk, the running walk, and the canter.  You see he won't trot because it simply is unnatural to him.  Before switching bits and potentially creating a larger problem, I strongly advise you to find a trainer in your area who has actual experience working with gaited horses.  The trainer will be able to see you two go, and he/she will ultimately be able to evaluate your needs better than I can online.