Try a reset of the breaker switch nonetheless... it's worth trying, once, in these circumstances.
The next question is, the condition of the belt on this treadmill.
The belt may need readjusting, and lubrication (with the special, non-grease, lubricant these treadmill belts generally require.)
The belt should be adjusted, generally speaking, so that it is loose enough that it does not quite slip, but nearly that loose.
If the belt is adjusted (or, has shrunk up with age, and lack of lubricant...) too tightly, then it can stop the treadmill from working or running. An over-tight treadmill belt can cause wear, or even damage, in many other ways, such as by overheating the motor.