What are the reasons for the car not responding at all when turning the key?

[Isabel]

Reason for a dead battery. Below are the signs before the battery fails: Difficulty starting the vehicle compared to usual: Requires more than one attempt to start, feeling like there's insufficient power. Vehicle idling: The headlights dim quickly from bright to dark, indicating the battery is low on power and needs replacement. When the battery is nearing the end of its lifespan: It can affect the alternator's operation. Usually, there will be abnormal noises from the alternator when starting the vehicle, typically a slight squeaking sound that may disappear in two or three seconds or even less. As the power decreases, the frequency and duration of this noise will gradually increase. Occasionally, after parking and attempting to restart, the entire vehicle has no power: This happens because when the battery is nearing the end of its lifespan, the starting current is insufficient, leading to increased oxidation at the battery terminals and resulting in a complete loss of power in the vehicle.