First map the pattern: one room, several outlets on one circuit, or roughly half the house. That distinction changes the likely cause and urgency.
Check for a utility outage
See whether neighbors or common areas also lost power and check with the utility when appropriate. A partial utility problem can look like an internal electrical failure.
Inspect breakers without opening the panel
A tripped breaker may sit between ON and OFF. Reset it once. If it trips again, leave it off.
Look for a tripped GFCI
A GFCI can interrupt several downstream receptacles, especially around kitchens, bathrooms, garages, basements, and outdoors. Reset only a dry, undamaged device.
Half the house plus very bright or very dim lights is a warning sign
That pattern can be consistent with a supply or neutral problem. Turn off sensitive loads if you can do so safely and contact the utility or an electrician promptly.
Do not remove the service-panel cover
Parts of the panel can remain energized even when branch breakers are off. Service and neutral connections are not homeowner troubleshooting points.
If there is smoke, arcing, a strong burning odor, or loud buzzing from electrical equipment, move away and use emergency services as appropriate.
Sources
- U.S. Consumer Product Safety Commission — Electrical Safety — Household electrical hazards, damaged receptacles, breakers, cords, and safe response.