Fluorescent lights can provide more illumination and for a longer period of time than a standard incandescent bulb. At the first notice that a fluorescent bulb is not working, go to the main service panel and check for a blown fuse or tripped circuit breaker. Diagnosing problems not related to a problem in the main power source is a little more difficult.
Listen to the sound of your fluorescent lighting when it is operating normally and you will be better able to determine when it is humming unnaturally. The cause of a humming fluorescent light is related to a problem with the ballast, which is a device attached to the hood of the lamp that looks like a transformer. Remount the ballast so that it is level if the fluorescent lamp is vibrating as well as humming. Replace the ballast if this does not stop the humming.
Look up and inspect the lamp closely if the fluorescent light does not come on or the middle of the tube is out but the ends light up. Several diagnoses are possible. The tube itself may be on the verge going out and need replacement. Make sure that the wall switch that operates the lamp is not faulty. A faulty ballast could also cause the light to fail to operate.
Find the starter switch on upper fixture and make sure it has not gone faulty if the problem is a flickering fluorescent bulb. After reinserting and testing the light, take it out again so you can match it up with a replacement starter if the light still flickers.
Wipe the tube with standard window cleaner and then dry completely if the problem is that your bulb blinks, flickers or takes too long to fully illuminate. Another diagnosis for this kind of problem is that the pins are not making efficient connections with the interior sockets. Take the tube from the lamp and use a toothbrush to clean off the pins, making sure you don't bend them. Blow away any debris that may be clogging the socket and then reattach the bulb.
Try leaving the fluorescent light on for longer periods when the problem is a light that takes too long to come on. The diagnosis in this case may be that the tube is not getting enough time to stabilise. Destabilisation of a fluorescent tube is often caused by use that is frequent but not for extended periods.