I'm Having a Partial Power Outage in my Home:

If you are experiencing a power outage in part of your home or a building, a common reason that your outlet(s) or light(s) are not working is a tripped circuit breaker. Circuit breakers trip when they are overloaded* or when there is a short in the system. This is to prevent an accidental electrical fire.

Note: Typical home electrical outlet circuits are rated for a maximum of 15 amps (1,800 watts). Here are some commonly used appliances and the amps/watts they use. Small, portable space heater-12.5 amps (1,500 watts), window air-conditioner-10-12 amps (1,500 watts), a 5 horse power vacuum sweeper-12 amps (1,500 watts), hand-held hair dryers-12-15 amps (1,850 watts). Often hair dryers added to the existing electrical load will cause the circuit breaker to trip.

Solution:

How to reset a circuit breaker. First, determine if the tripped breaker was caused by a new electrical load, and unplug the new source immediately. Next unplug all of the other electric loads or appliances on the dead circuit in the event that one of them may be the culprit for the overload. To reset a circuit breaker, the switch must be pushed all the way to the "off" position and then returned to the "on" position. Then one time, plug the appliances and electrical loads back in to see one of them is the trouble maker. Be sure you don't overload the circuit a second time. Leave an item or two unplugged or move them to another part of the house or building. This should take care of the issue in most cases, and you will save yourself as much as $150.00 by not having to call a professional just to reset your breaker.

Could I Have a Short Somewhere?

If doing this does not restore power you may have a short somewhere, either in an appliance or in your internal wiring. If this is the case then your circuit breaker is doing what it is supposed to do by cutting off the electric supply to a damaged wire. Don’t keep trying to reset the breaker if it trips more than twice, call the electrician to repair the problem.

I replaced my circuit breaker and now it is tripping more frequently:

Be especially cautious if you are able to plug many appliances into older electrical circuits and they don't trip.  Often, older circuit breakers get "stuck" and may not trip when they are supposed to.  Sometimes after replacing an old circuit breaker the homeowner will complain that now when they plug in the space heater (microwave, vacuum cleaner, hairdryer.....) the ciruit trips but it didn't do that in the past.  This is actually GOOD.  Circuits are supposed to trip when you overload them.  They are doing their job and protecting your home.

We often see circuit breakers installed that are larger than they should be for the wiring they are protecting.  This is done to prevent the breaker from tripping when the circuit is overloaded.  Yes, you will have fewer tripped circuits, BUT at the risk of overheating the wire and endagering your home.  If you have applicances that use a lot of wattage, your best bet is to add additional circuits to safely handle the additional electrical load. 

My Breaker Box is Buzzing, or Humming:

A good indication that you have a short somewhere is you may hear a buzz or a hum when trying to reset the breaker. You may even see a flash of light, and the breaker will not stay in the "on" position. If the short is in an external electric load or appliance, the breaker will stay on until you plug the faulty source back into the outlet and turn the switch back on. That is why it is helpful to unplug everything before resetting the breaker and then plugging them back in one at a time. You will easily find the source of the short when you plug in and switch on one appliance at a time. When you determine which external electric load or appliance has the short, remove it from the plug and you should be able to reset the breaker and restore power.

My Breaker Refuses to "Reset":

If the breaker refuses to reset while all appliances and electric loads are unplugged from the circuit, then you may have a short somewhere in your wiring.

Note: a nail or screw that is put into a wall can sometimes hit the internal wiring and cause a short.

For a short in your internal wiring you need a qualified electrical contractor to fix the problem.