When you turn the key in your car and nothing happens, there are a number of reasons the engine won't turn over. Most often, a dead car battery is to blame, but the alternator, starter, spark plugs fuses or other parts could be the cause of the problem.
If the ignition offers a clicking noise when you try to start the engine, this usually points to a dead battery. It could also indicate a loose connection to the starter. After you've tried jumping the battery to no avail, inspect the wires connected to the starter. The owner's manual can point you in the right direction if you're unsure where the starter is located.
When you are met with silence, the battery might be the source of the issue, but not necessarily dead. Pop the hood and check out the terminals. Corrosion around the terminals could be affecting the transfer of power from the battery to the cable. You will need to clean the terminals, which can be done with a bit of baking soda, water and a hard bristle brush. Just make sure to disconnect the cables before doing so, starting with the negative, or ground, wire and then moving on to the positive wire.
When the engine cranks but does not catch, you may be out of fuel. The alternator will be able to start the engine, but without gasoline in the engine, the combustion process cannot continue. Alternatively, there might be fuel in the tank, but the spark plugs are worn out. Spark plugs provide the catalyst that ignites the fuel in the combustion chamber, so if they're not working, the engine will not run either.
To inspect the spark plugs for damage, you must first remove the wires. Consult the owner's manual to determine their firing order, which is the order in which they were installed. Be sure to label the wires so they are put back in the same manner. You will need a socket wrench to remove the plugs, doing so one by one.
Upon removing a spark plug, examine the well it came out of for signs of oil, dirt or other debris and clean it if necessary. Then, examine the end of the plug that was in the combustion chamber. There should be a small metal hook with a tan coloration coming off the end. If it is at all dirty or damaged, you may need to replace it. When replacing one, it is best to replace all, as one failure may indicate the others are about to break or fail soon as well.
An engine that starts but dies shortly thereafter could have problems with the fuel injection system or the carburetor on older models. If the fuel injectors are clogged, not enough gasoline is getting into the combustion chamber and the engine won't be able to function properly, resulting in a stall.
Other possible causes of a car that won't start include a damaged distributor cap, faulty fuel pump or clogged fuel filter. If your car seems to only have trouble starting on rainy days, dampness on the distributor cap could be the source of the problem. To dry it out, remove the cap, flip it upside down and spray the damp part with mechanic's solvent. Let it soak for a moment before pouring it out and then use a clean rag to dry the cap thoroughly before replacing it.