Final answer:
When a car won't start with a full tank of gas, one should use the scientific method for troubleshooting, beginning with the simplest explanations such as a dead or disconnected battery. If initial checks don't solve the issue, further inspection of the ignition system or seeking professional help would be the next steps.
Step-by-step explanation:
If a driver inserts the key to start his car and the car does not start, even though the car has a full tank of gas, the next logical thing to do is to diagnose the problem systematically using the scientific method. Checking for common issues with the ignition system, battery, and electrical connections can help determine the cause of the problem. For instance, if the engine does not turn over and no dashboard lights come on when the key is turned, it suggests an issue with the battery or its connections. One might first check to see if the battery terminals are clean and tightly connected. If the battery is the problem, a replacement or a charge may be necessary. If the battery terminals are corroded, cleaning them might restore the connection.
It's important to remember that troubleshooting should be systematic, moving from the most common and simplest to fix issues (like a dead battery) to the more complex ones (such as a faulty starter motor). If inspecting the battery doesn't solve the issue, it could be a problem with the starter motor or the alternator. If the car's ignition system is the cause, inspection of the spark plugs, distributor cap, rotor, and ignition wires might be the next steps.
If basic troubleshooting does not resolve the issue, it is advisable to seek professional help. A mechanic would have specialized diagnostic tools and expertise to troubleshoot complex car start issues.