You most likely have a loose wire from a push-in connection. Check the receptacles for loose wires and replace using the screws instead of the push-in. The problem may be on a receptacle that is still working.

The first place I'd check is the circuit breakers or fuses. Sometimes a tripped circuit breaker is hard to see. It trips to a mid-position and needs to be switched all the way off, then back on. Only reset a circuit breaker once. Repeatedly attempting to reset a tripping circuit breaker can cause damage to your wiring and possibly start a fire.

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