Frozen unit

Try to reprogram the address just in case. Try it on someone else track if you can. Try running it in conventional mode.

   All IMO;  Don

I am no expert. If it were mine I would take the shell off and check the connectors, beyond that I would find someone to repair it.

   Do other locos work on the same track? If so it is probably time to have someone look at it for repair.  Don

If it is one of the early Legacy engines, it has the modular boards.  Chances are your R4LC needs to be reseated.  Very  common problem.  I had two of them this week with the same issue.

Marty's suggestion is first on the list if you open up almost any engine for problems.  Loose connections and broken wires are one of the most common issues.