A car that won't start can have many causes, from simple to super expensive.
Before you have your vehicle towed, have your checked the battery cables? If they are corroded, that could be your problem. The corrosion may be preventing your battery cables from making contact with the battery.
Corrosion will appear as a whitish powder where your battery terminals connect to the negative and positive posts on your battery. The substance is composed of sulfuric acid and hydrogen crystals that form when your battery gives off gas.
You can clean it off yourself, but it's important to take certain precautions first, because sulfuric acid will burn through your skin and clothing if you touch it. First, make sure your engine is turned off. Then, use a wire brush to brush off the sulfuric acid powder.
Starting with your negative terminal (your battery should be marked with a plus and a minus symbol at each terminal), loosen the nut attaching the cable to your battery with a wrench. Then pull the cable from the post. Repeat this process with the positive cable. Don't touch other metal parts of your car while doing this to avoid shorting out the battery.
Check the battery for cracks and the cables for signs of damage. Replace them, if necessary.
You're now ready to remove the corrosion. Mix equal parts water and backing soda to form a paste. Scrub the mixture into the corrosive build up using an old toothbrush or wire brush, reapplying as needed. Then, spray off any residue with a spray bottle full of water. Dry the terminals and clamps with a rag and lubricate the petroleum jelly to prevent future corrosion.
Important: Make sure you connect the red cable the positive (+) terminal and the black cable to the negative (-) terminal or your battery could explode upon starting.