Ensure treadmill is connected to dedicated 120v, 20 Amp circuit.
Inspect all drive motor wiring and connections. Repair any damaged wiring and reset any connections as necessary. Using an ohmmeter, test for an open (infinite) reading and if the reading is open, replace the drive motor.
Inspect the drive motor pulley and drive belt for damage. Replace if necessary.
Inspect all cable connections to the motor controller. Reset any connections as necessary.
Test unit with a known good motor controller. Replace if necessary.