Why won’t it start battery n alternator both good

Hello, I'm not sure I understand what is happening here. When you turn the key is there anything that happens? Do the lights on the dash turn on? Does the engine crank over but not start? Or is there no noise at all? Your alternator doesn't figure in at all until the car is running. The focus here should be on what is preventing the engine from starting in the first place. The alternator can be tested for output when the engine is running at 2,000 RPM. If the battery is fully charged and the engine is not cranking, you have a cable issue, starter motor issue, shift lever position sensor issue for an automatic, clutch pedal sensor for a manual transmission or ignition switch issue. Hands on testing is required. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops