When your attempts to start your car fail, it can sometimes be difficult to ascertain the true cause of the problem. The most frequent cause will be a dead battery. Occasionally, though, your car may not start because of something wrong with the mechanical systems of the car. At times, you might need a trained mechanic to discover what is wrong, but there are always things you can and should do before taking the often expensive step of visiting an auto shop.
Turn your ignition key to the "accessory" position. If your battery is functioning, this should feed electricity, directly from the battery, to certain accessories within your car, such as your radio. If these do not work, it is probably a battery problem.2
Turn on your headlights. If they do not come on, or if they are dimmer than usual, it's probably a battery problem.3
Attempt to start your vehicle. If your starter attempts to turn over but your electrical systems cut out, your battery likely has just enough juice to power your accessories, but not enough to start your car.4
Attempt to jump start your car. This entails connecting your car's battery to another car's battery with jumper cables, and attempting to start it. Please note that the second car should not be running when you attach the cables, but should be running when you attempt to start your car. The jumper cables will transfer electricity to your car, from the other car. If your car still does not start, the problem is more than likely not with the battery. Replace your battery if jump-starting your car works.