Car Key Cannot Start Engine

Causes

Dead battery: This is the most common cause of a car key not being able to start the engine. If the battery is dead, there is not enough power to turn over the engine.
Faulty starter: The starter is responsible for turning over the engine. If the starter is faulty, it will not be able to turn over the engine, even if the battery is good.
Ignition switch problems: The ignition switch is responsible for sending power from the battery to the starter. If the ignition switch is faulty, it will not be able to send power to the starter, even if the battery and starter are both good.
Security system problems: Some cars have security systems that prevent the engine from starting if the correct key is not used. If the security system is faulty, it may prevent the engine from starting, even if the key is correct.

To diagnose the cause of a car key not being able to start the engine, you will need to:

Check the battery: Using a voltmeter, check the voltage of the battery. If the battery is dead, it will need to be replaced.
Check the starter: Listen for a clicking sound when you turn the key. If you hear a clicking sound, the starter is probably faulty and will need to be replaced.
Check the ignition switch: Using a voltmeter, check the voltage at the ignition switch. If there is no voltage at the ignition switch, the ignition switch is probably faulty and will need to be replaced.
Check the security system: If your car has a security system, try disabling the security system and then starting the car. If the car starts with the security system disabled, the security system is probably faulty and will need to be repaired.

Once you have diagnosed the cause of the problem, you can repair it.

There are a few things you can do to prevent your car key from not being able to start the engine:

Keep your battery charged: Make sure your battery is always charged. You can do this by driving your car regularly and by keeping the battery terminals clean.
Have your starter checked regularly: Have your starter checked by a mechanic every year or two. This will help to prevent the starter from failing prematurely.
Have your ignition switch checked regularly: Have your ignition switch checked by a mechanic every year or two. This will help to prevent the ignition switch from failing prematurely.
Keep your security system in good working order: If your car has a security system, make sure it is always in good working order. You can do this by having the security system serviced by a mechanic every year or two.

By following these tips, you can help to prevent your car key from not being able to start the engine.