I picked one of the Lionel remake version a couple of years ago NIB and it did the same thing, the motor ran but nothing happened.
I had to strip it down and found the belt had set itself to the shape it went around the motor pulley. I put the belt in some warm to hot water and managed to bring the belt back to its original oval shape and it ran fine again.
if it is used on a frequent basis then the belt won’t get an opportunity to set it self to the curvature of the pulley again.