When you turn the key in the ignition and the engine roars to life, there are a number of different components that help get your car running. This includes the battery, the alternator and the starter, and if any of these parts are malfunctioning, you may find your car is just a gigantic hunk of immovable metal. In most cases, a car that won't start can be traced back to the battery, but if this is not the source, you could be looking at an issue with the starter.
The starter is in place to crank the engine and get all the parts moving at the appropriate speed, and it replaced the original hand crank that was used on early automobiles. Most modern cars are equipped with an electric starter, which uses a solenoid switch to get going when you turn the key.
When battery power is delivered to the solenoid switch, it activates the starter, which hooks up to the engine's flywheel. This part is designed to store rotational energy that is greater than that being supplied by the starter. The stored energy builds up until there is enough for the engine to turn over and start running. Cranking the starter also helps to power the crankshaft position sensors that get the fuel injectors and the spark plugs going to facilitate combustion and propel your car.
There are a number of issues that could affect that starter. If you drive a car with a manual transmission, make sure your foot is on the clutch pedal, as there may be a safety switch that locks the starter if the clutch pedal is not depressed. When you turn the key in the ignition and you're met with silence, chances are the starter motor is dead and you'll need to have the part replaced. However, it could also be due to a faulty solenoid or a bad wiring connection.
If you hear a clicking or a whirring sound, this means the motor is working, and there is another issue preventing you from starting the car. You can bypass the solenoid with jumper cables to see if the starter motor is working. If it is, you may need a new solenoid or there could be a problem with the ignition circuit. A bad solenoid could harm the starter, so you may want to have a professional check the part for signs of damage when you have the solenoid replaced.