the tredmill is stuck in Interval Hills mode. I can start the tredmill in this mode but I can not stop it using the stop button. When I try to change modes, only two of the other modes seem to respond to me pressing the button. When I release the button it returns to Interval hills mode. I cannot change users, the speed, or the elevation ( I can hear the beeps when I press some of the buttons but no action is taken).