When your dog is refusing to walk just sit and wait with a treat and try and lure the dog forward with the treat.
He should eventually start walking but if not just stand or sit where you are and wait until he or she eventually starts moving.
Sometimes you may have to give a little tug and put a little pressure on the leash to pull them towards you to get them to walk.
When your dog does move then toss a treat for them in the direction you want the dog to walk.