If your vehicle won't start, it's usually caused by a dying or dead battery, loose or corroded connection cables, a bad alternator or an issue with the starter. It can be hard to determine if you're dealing with a battery or an alternator problem.

What causes a car to turn on but not start?

If the car cranks when you turn the key, but the engine won't start, it could be because fuel isn't getting to the engine. One potential reason for this could be dirty fuel injectors. ... Once clogged, the fuel injectors may not add the correct amount of fuel to the cylinders, and the vehicle may not start up at all.

How do you tell if its your alternator or your battery?

If your engine won't turn over or takes far longer than usual, it's time to grab the jumper cables and attempt a jump-start. If your engine starts and stays running but won't start again later, it's likely a battery problem. If your vehicle immediately stalls, it's probably a bad alternator.