My hot water stopped working in one bathroom, what can I try in order to fix it?
If you're getting hot everywhere else, but not in the bath, then the hot water flow has been interrupted.  Check the shutoff valves in your house - the most likely suspect is that someone's turned one off (possibly as a prank).

If all the valves are confirmed open, then the next question is, what kind of water lines do you have?  If you have galvanized pipe, it's known to corrode, so a possible culprit would be a buildup of corrosion in the line to the bathroom to the point where no or almost no water flows.