Track problems -- short circuit?

[Charlie B]

Rob,    check first for something on the track that is causing a short. (You do have a short from the sounds of your post) something may have fallen from the train. If nothing there check all turnouts if you have any and make sure the frogs and points have not shorted. The next step would be to remove the switch wires one by one. 
      A defective switch is possible because it was sudden, but the turnout and metal shorting the track cn do likewise.
Charlie