If an electrical outlet in your home has suddenly stopped working, your first instinct is probably to check the circuit breaker that it is connected to. If it turns out the circuit breaker hasn't been tripped, then you may be dealing with a more difficult problem. There are a number of different reasons why an outlet will stop functioning without tripping the breaker. Some of them require the attention of a professional electrician. Others you can do yourself.
Many modern electrical power outlets are equipped with ground-fault circuit interrupters, or GFCIs. These devices are included in the outlet to reduce the possibility of electrocution. When the GFCI senses a current leak, it disconnects the terminals inside the outlet, cutting off power to it. You can tell if your outlet has a GFCI by the presence of a "Test" button and a "Reset" button. A random passing event such as a power surge can cause a GFCI to trip. Push the "Test" button to ensure power has been shut off to the outlet; then press the "Reset" button to restore power.
Hidden Tripped GFCI
If this fails to work, or if your outlet does not have a GFCI, then you need to look at other outlets. Sometimes a GFCI in one outlet is responsible for protecting several other outlets further down the line from it. Look in other rooms, closets, hallways and anywhere else you might have a GFCI . Hit the "Test" button, then the Reset" button, on each of them and keep going back to find out if this has fixed your problem.
It is possible that the reset button on the GFCI is broken or that the wiring inside the GFCI is broken. In this case it will have to be repaired or, more likely, replaced. Contact an electrician for help with this work if you do not have proper electrical wiring training.
Of course, the issue might not be the GFCI at all. If one of the wires or contacts in the outlet, or in the wiring to or from the outlet, is broken, there isn't a complete path for the electricity to travel. In such a case, the outlet will not work even though it has not tripped the circuit breaker. You should be particularly concerned that this is the problem if you have had recent work done on the outlet, the wall around it, or anywhere else on your home's electrical system. It's likely that a professional electrician is needed to properly diagnose and repair this problem.