Make sure the wheels turn freely by hand. Clean all the wheels and the pickup rollers with naphtha. Put the loco on the track and apply power. See if the headlamp lights. If the loco does not move, turn power on and off to see if the reverse mechanism is working in the loco. If not, move the lever on top of the loco to the opposite position and apply power again, cycling the power as above.
If the loco does not run, it will need servicing.
Larry