Lego remote controlled cargo train not working
The best way to solve this type of problem is to break it down and isolate the fault.

You might find that it is easier to remove the Power Functions components from the model for some of the following:


Check all connections. Disconnect each cable and re-connect everything. Ensure that the plugs are the right way around (they don't sit right if not) and that they are pushed on properly.
Check that none of the cables are damaged.
Connect the battery box directly to the train motor, bypassing the IR receiver. Does the train work now? If so, the problem is either the remote or the receier. If not, the problem is either the battery box or the motor.


Remote / IR Reciever Problems

If the problem is with the controller / IR receiver:


Make sure that there is nothing blocking the signal between the controller and the IR receiver. Avoid bright sunlight.
Check that both controller and receiver are on the same channel. There is an orange 4-position switch on both the IR receiver and on the controller, and this determines the channel. Leaving one switch alone, try all 4 positions on the other.
Check that the batteries are inserted correctly in the remote. Take them out and put them back in again.
Check that the batteries are aren't worn out. Sometimes even new batteries don't deliver the correct voltage. If you have one, test your batteries with a volt meter. If not, try swapping them with new batteries, or test the batteries in something else to make sure they're OK.
Check that the battery terminals are not corroded. Sometimes corrosion isn't obvious. Try taking the batteries out and putting them back in again, or twisting them around until they may contact.
You may be able to check that the controller is sending a signal. Although you can't see the flashes of IR light yourself, you may find that you can use a digital camera (such as a mobile phone camera) to see the flashes of light when you use the controls on the controller.


These images are from the LEGO web site, which contains more information on both the controller and IR receiver:




Battery Box / Motor Problems

Check the batteries in the battery box, following steps 3-5 above. The little green light should come on when they're OK and the battery box is switched on (the green button is the on-off switch).

There is a great description of the battery box on the LEGO web site, which might help explain things better than I can. This picture is from that site:



If All Else Fails

Contact LEGO customer services. They'll be deligted to help.