1. Battery: The battery may be weak or dead. Try jump-starting the car using another vehicle or a portable jump starter. If the car starts, it is likely that the battery needs to be replaced.
2. Starter: The starter may be faulty. If you hear a clicking noise when you turn the key, this is a sign that the starter is trying to engage, but is unable to do so. The starter may need to be replaced.
3. Fuel Delivery: There may be a problem with the fuel delivery system. Check the fuel level to ensure that there is enough gas in the tank. Also, inspect the fuel lines for leaks or blockages.
4. Ignition Switch: The ignition switch may be faulty. If the key turns, but the car does not start, this could be the cause. The ignition switch may need to be replaced.
5. Security System: The car's security system may be malfunctioning. Try unlocking and re-locking the car using the key fob. You can also try disabling the security system by following the instructions in your owner's manual.
If you are unable to identify and fix the problem yourself, it is best to have the car towed to a qualified mechanic for diagnosis and repair.