Perhaps only a fender bender that mars a pristine paint job is more frustrating than turning your car's ignition key and getting no response from the engine. Knowing some common reasons why your car won't start can help you troubleshoot the problem and identify the cause:
Fuel System Issues
Two possible culprits here are the fuel pump and the filter. If the filter is partially clogged, the car can hesitate and stall repeatedly. If the filter is completely blocked or if the fuel pump has failed, the engine will crank but it won't start.
Bad Ignition Switch
This switch is what allows electricity from the battery to reach the starter so it can spark and ignite the gas. If it's gone bad, the dash lights can flicker, the radio and other electrical accessories may not work or you may have difficulty turning the ignition key.
If the starter wears out, you'll hear a high-pitched screech or a clicking sound when you turn the key. When it goes bad, the starter motor actuates but doesn't spin, so it can't create the spark needed to get the engine going.
If the engine is ghostly silent when you turn the key, the most likely cause is a dead battery. It's easy for a battery to drain and die due to a bad alternator or if you leave the lights or any accessories on for a long time, but you should be able to jump-start and recharge it. If the battery is past its expiration date, though, you'll need to replace it to get the engine going again.
The alternator powers the car while it's being driven, and it recharges the battery too. You'll typically have some warning that it's going bad, such as dimmer lights, slower power accessory operation and a lit dashboard indicator. If it fails completely, the battery will drain and the car simply won't start.