I just repaired such a treadmill, with report of motor not working. All that was amiss was that the motor brushes were warn out, replaced in 10 min job.
In this case the motor would stop /start if the belt was moved.
1 DISCONNECT mains plug
2 Check you have DISCONNECTED mains plug.
3 Unscrew the small screws (Prob, 6) of motor cover.
4 Slide off cover.
5 Unscrew black plastic motor brush plugs(2)
6 Pop out old brushes, insert new ones.
7 Replace plugs,cover and screws.
Ken J H