If the lighting in your aquarium has stopped working, the problem could have many causes, but in many cases, it is either the bulb or the solenoid. Replacing the solenoid on you aquarium strip light will have your aquatic environment back to normal in no time.
Replacing an Aquarium Light Fuse
Turn off the light and unplug it from the wall.
Remove the light from the aquarium and put it in a dry place where it can be worked on safely.
Locate what seems to be a fuse, but is actually a solenoid or a starter.
Turn the solenoid counterclockwise until it pulls free.
Replace the old solenoid with a new one. They are readily available at most pet stores.
Return the light to the aquarium and plug it back in to the receptacle. Turn on the light.