Hello, the usual culprit is the fuel filter being clogged. Sometimes a clogged fuel filter will let the fuel through and other times it will not. This means the car will run some of the times, where other times it will starve your engine of fuel causing it to stop and not start right away. The next possibility is your ignition system. Cracked distributor cap, a short in that area, bad coil wire, or any other obstacle causing your spark to not reach the spark plugs. Easiest and cheapest place to start is to replace your fuel filter and eliminate that as the cause. Your fuel pump could also be the issue but you can usually hear a whirring sound before you start a car which is the fuel pump doing its job. Hope this helps.