Circuit is Dead but Circuit Breaker Isn't Tripped
When the power goes out in a room or in a series of outlets, the culprit is usually a circuit breaker or fuse has blown. However, in some cases the breaker or fuse may seem fine. You can reset the circuit breaker but the circuit is still dead.
Caution: Please read our safety information before attempting any testing or repairs.
This phenomena can occur in homes that use GFCI (Ground Fault Circuit Interrupter) outlets. The GFCI outlet (sometimes also called a GFI) is like a circuit breaker and can shut off the flow of electricity to the outlet and all devices downstream of the outlet. When it senses an imbalance it will trip, much more quickly than a circuit breaker. Its purpose is to protect people from electrocution, something the average circuit breaker can't do.
One thing about GFCI outlets, is that they can control outlets and lights in other parts of the house than where the GFCI is located. It is quite common for a GFCI to be tripped in a bathroom, kitchen, laundry room, closet or even outdoors and another room somewhere else in the home to be affected. Don't assume the GFCI is even on the same floor and the affected area.
How To Reset a GFCI Outlet
Before electricity can be restored, the GFCI must be reset. However, even before you do that, you must take steps to ensure that it is safe to do so. Turn off or unplug all of the devices that are plugged into the circuit. Make certain no dangerous condition exists before restoring power.
Press the "Test" button. If it does not click, then it was tripped. Now press the "Reset" button until you feel it click. Once done, power to the circuit should be restored.
Follow this link for more information about GFCI Outlets