If you had strong headlights and the car eventually started, I would suspect a bad ground or power wire leading to the passenger compartment is at fault. Check under hood first where power parts way into interior then cafefully check all grounds that you can find( remove to inspect and clean is the best way). Good luck. Also don't rule out a faulty ignition switch (where key goes in)...they are relativley high maintenece parts and when at fault, will do just what yours is doing.