If your belt is sticking, it's usually that it needs lubrication or the walking belt is worn. I don't think it's the motor, but the best way to check is to run the machine for 30 mins without anyone on it. If you don't hear any variation in speed, it's a friction issue.
If that is the case, I would loosen your belt a little, stick your hand palm up underneath, and run it from left to right. You are feeling for 2 things. Texture and lubrication. The texture should be like a canvas or screen door. You shouldn't have any smooth spots. If you have smooth spots or there isn't any texture, replace your walking belt.
The 2nd thing you are checking is for lubrication. Your hand should be greasy after your check for the texture. If it's dry and the texture is good, I would call the manufacturer and get some lubrication. Do Not use silicone spray because it will destroy your belt and the walking platform.
Good luck!
nordicgirl
June 2009