When your Ford Fiesta won't start, it could be for a number of reasons. The first thing you should do is establish why it won't start, and then fix the problem. Often, when determining why it won't start, you should check basic things first.
Check your battery. If it does not even crank when you turn the key, there is a good chance the battery is depleted. The simple way to test this is by switching on the interior or exterior light, radio or cigarette lighter. If they work, it's not the battery. If they don't work, you need to either charge or replace the battery.
Check that you have gas in your car. It sounds simple, but it is easy to overlook. Check by turning the key to the ignition position and then checking the gas gauge. If the tank is empty, take a gas can to a petrol station, and use it to fuel your car.
If the key won't turn at all, the car might be immobilised. To solve this, close all of the doors, lock the car, and then unlock the car. This happens because the key must be turned within a set period of time (usually 30 seconds, but varies through the range) otherwise the car will be immobilised for security reasons.
If you have an older model with a choke, it is possible the engine is flooded with gas and can't start. To solve this, remove fuse 19 from the fuse box, and then turn over the engine. Removing the fuse disables the injector, and turning the key burns off excess fuel. Replace the fuse, and the car should start.
If the car cranks but does not start, it is likely the fuel pump needs replacing. When you turn the key to the ignition point, you should hear a whirring noise, which is the fuel pump switching on. If you do not hear it, it needs replacing.
If you hear a clicking sound while cranking, you have a faulty starter motor. If you are confident, starter motors can be replaced at home without any specialist equipment.
Check your spark plugs. If they are dirty, they will not spark properly, and this will cause the car to not start. Additionally, they might need replacing if they are worn or not firing properly.
Prevention is better than cure, so keep your car regularly serviced, and you will have far fewer problems with it.
You might be able to jump start your Ford Fiesta if the battery is dead, but this is only a temporary solution.