How do I troubleshoot a ceiling fan that suddenly stopped working?
Well for starters you can check the power at the switch to see of the switch has failed. This can be done with a power line wire test probe.....but do use care when dealing with AC power. It is dangerous stuff and can injure or kill if not handled properly. If this leaves you with a queasy feeling then now would be a good time to call in a professional electrician. 

If power is passing through the switch to the fan and light unit then it is a pretty good guess that something has gone wrong with the unit itself. There are many things that could happen and some of them may be dependent on just what type of ceiling fan unit this is. For example if the fan was one of the type suspended down from the ceiling on a pipe type thing and if the fan was somewhat unbalanced a continual swinging motion of the hanger pipe could cause the electrical wires to fracture and become open circuit. Without further detail as to the type of fan it would be difficult to suggest specific failures that you might expect to see.

Do note that it is common that a fan / light assembly may have separate switched power leads for the fan and for the light. However there may be a common return neutral line. Since it seems like both the lights and fan failed at the same time it is likely that the wiring failure could be in this common return line.