years ago I had a machine freeze up on me...took it into the shop and guy asked me when the last time it was oiled???oiled like in a car???? I was so dumb, have learned since. LOL he oiled it and held the foot pedal down and after about 5 minutes it started to move...he said "man that sucker was dry" you can believe I never did that again...could this be the problem with yours????