Tools Required:
Mulimeter
DC Power Source (One with a high enough amp rating like a power drill battery)
Meter Test (Simplified)
1) Testing Low (close to 0) Resistance between the motor leads (Red and Black)
2) Testing Infinite resistance between either red or black motor lead with respect to chassis ground.
Great video about this procedure Here
If you do not get the result described above, Replace your drive motor.
Drill Battery Test
Very simple, we are removing all variables "before" the Motor, such as the motor controller, power entry components, or even the power source itself. Check it out.
Note, you will have to source/fabricate wires that connect into the drill battery and motor lead wires. If you view this as too much effort or you don't undersand, you should probably be using a technician in the first place, no offense. Here's a database of technicians
Anyway, this is a great video that exemplifies this procedure - Here
Obviously, if the motor works with said independent source of power, your motor is fine, move on to power components and continuity.
Treadmill Motors AND controllers die due to high Friction Coefficient which stems from lack of maintenane to the belt and deck.
Related:
Technician Database, Testing Power Components, Friction Coefficient - The Enemy Within, Save your Treadmill from The Fitness Graveyard