Check your circuit breaker or fuse box. If there is a tripped breaker or blown fuse, reset the breaker or replace the fuse.
If there is a nonworking outlet and no fuse has blown or circuit breaker tripped, check for a tripped GFCI. A GFCI may be wired in a branch circuit where other outlets share the same circuit and fuse or breaker.
The nonworking outlet may be down the line from the GFCI and not even located near it. A branch circuit device does not protect anything plugged into it, but it does protect everything down-line from it.
Locate the tripped GFCI. If you are having difficulty finding it, check a main floor guest bathroom, an entryway closet, a walk-in closet or the garage.
Until 1987 the code required only one GFCI to protect the whole house.
Press the "Reset" button on the GFCI after you have located it. This will reset the outlet, and all outlets down-line from it should be working.
If it won't reset, press the "Test" button, then press the "Reset" button. If it doesn't stay reset, there is most likely a faulty outlet or device down-line from the GFCI.
If not, the GFCI device may be defective.