how can I repair my pro form 835QT treadmil?

As soon as I step on it, it stops running, I have lubricated the belt,but it didn't help. I put it on high speed and it spins well- however i step on it and take no more than 6-10 steps I here a click and it stops. I remain on it and I here a click and it starts again - I take 3-4 steps and it stops. Does the belt need to be replaced or is the motor or power supply going bad?