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The solution that you should try first, is that the belt needs 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.
Belt lubricant is usually a sort of silicone powder. It has no regular (grease/oil-type) lubricant in it.
Belt lubricant is applied to the belt, simply. All over, spread around.
And you can buy it, here:
and it is the sort you really need:
1. for the belt, not other parts
2. for treadmills, of more than one brand or type.