There are many reasons that a car won't start, but one possibility lies with a little-known auto part called the neutral safety switch. Essentially, this switch is present in all automatic transmission vehicles to prevent the engine from being started when the car is in any gear other than neutral or park. Starting the engine while in a different gear would cause the vehicle to immediately start moving and could be extremely dangerous, so the safety switch's job is to prevent such an incident from occurring.
Unfortunately, if the switch falls out of alignment, it can potentially prevent the vehicle from starting at all. Unlike other electrical switches in the car, the neutral safety switch is connected to the vehicle's gear shifter. This essentially closes the circuit when the car is in neutral or park, but opens it when it's in any other gear.
The switch is typically held into place with screws, but these can come loose or degrade over time. If this happens, the switch may disconnect from the shifter or simply become misaligned, which can lead to issues getting the car started. Many drivers with a neutral safety switch problem might find that they can start the car from gears that they are not supposed to, or the car might start if they hold the shifter in a certain way. Sometimes it simply might take several tries to start the car, but it does start eventually. This can help rule out problems with similar vehicle parts, such as the battery or alternator.
Still, the best way to actually test a neutral safety switch is to locate the part yourself. Use your owner's manual to locate your neutral safety switch - it is always connected to the car's starter solenoid, but the placement can vary. Put your key in the ignition, but don't turn the engine on. Then put your car in the "reverse" gear, making sure to apply the parking brake and chock the wheels so the car doesn't roll.
Disconnect the wiring connector from the switch, then use a 12-volt test light or circuit tester. If the bulb lights up, then the problem is most likely not with your neutral safety switch. However, if no power is flowing through the wiring, then it's likely that the neutral safety switch is your culprit, and it will require replacing.