1 Answer

ALWAYS start by checking to see if the bulb is still viable, after making sure the switch is ON. To know for sure, replace the bulb with one you KNOW works.  If the good bulb doesn't come on and you KNOW you have the switch ON, time to check to make sure the corresponding BREAKER is on.  
If all those are in working order (although your switch may need replacement/rewiring), it's time for an electrician.  Checking the wiring for the switch involves removing the plate and making sure the wires are still connected to the switch.  You DON'T want to touch that unless you know the switch is OFF.  Best way to reassure yourself on THAT is to turn OFF the corresponding breaker.