I bought the same train set for my grandson. It did the same thing your loco is doing. I looked in the instruction manual and one of the troubleshooting tips was to check if the headlight was on, but the engine made noise and didn't run. It said to check the track end of the feed wire for continuity. Sure enough, we fixed this and it's running fine.

find a couple of pieces of wire and attach these to the power pack.

Make sure you have the track wired to the correct terminals on the power supply. There should be two sets; track power and accessory power. The accessory terminals supply ac power at a fixed voltage around 15 volts. This will not run the DC motors in the locomotives. The track power is a DC current that is regulated with a rheostat.
You can test the engines by turning them upside down and applying one wire from the power supply to one set of wheels (say on the right side) and the other wire to the other set of wheels.
Jon

I need to remove the shell on a new Bachmann EMD F7A so I can install decoder. Can anyone help. I have tried spreading the sides to clear the tabs, but the frame doesn't move from inside the shell.
Thanks for any help.
Jon