Transformer Problems

[STLEngineer]

Newbie here.  Need help with Christmas train we just bought.  We got the train up and running and everything was fine.  Powered on again and the train will only operate at one speed.  The changing speeds on the transformer does not work.  Can set it at any speed and it does not change.  Any ideas on what we may be doing wrong?

[the Bach-man]

Dear STL,
Make sure you don't have the AC terminals connected- if you do, and it's a DC loco, the one speed will soon be... stopped!
Be sure you're using the variable DC terminals.
Have fun!
the Bach-man