Thank you for responding so quickly.  Lead truck has not turned.  What else may cause the loco not to move, but the light to work with no problems?

Recently purchased a Large Scale 7th Avenue Holiday Express.  After assembling, it worked for maybe 20 minutes.  Checked and rechecked everything according to the DVD and it still is not moving.  When we turned the dial on the speed controller, the light comes on, but the train does not move.  Please help.