Another possible cause is that corrosion might have occurred in the socket where the bulb should enter. So turn your mains power off and inspect the socket. Do not put your fingers in there! After turning off the breaker, clean the connection using a cleaner or even sand paper. Also make sure that connections are not smashed down and that no contact exists with the bulb at the bottom. You will need to replace either the light fixture or all the wires if you realize that your down light is broken. If these wires are corroded beyond reasonable repairs, it is wise if you replace them using a licensed electrician.
Adapt the correct procedure:
The following procedure is the most standard and so far the safest to adopt.
1. Test the bulb and change it if necessary.
2. Remove the bulb.
3. Ensure that the circuit breaker is not tripped.
4. Put back the cover plate and turn on the circuit breaker. Proceed to the next step if no positive results are recorded.
5. Turn off the breaker and remove both the cover plate and switchboard. Then use a tester to test for continuity.
6. Replace the switch if it is defective.
7. If you find that the switch is ok, proceed by first removing the cover plate from the light fixture. Caution: make sure that the wires in the electrical box are not charged. Then complete the job by replacing the light fixture.