Some things you can try if your car will not crank. These are tests that you can perform without any test equipment. It is a standard list that I send out to quite a few people. Some items on the list may not apply to your situation.
1. Put the car in neutral and try to start it.
2. Make sure your battery terminals are securely attached to the battery and that they are not corroded. Loose or dirty battery cable terminals cause a bad connection and are a common cause of a no crank condition.
3. The problem could be with the key not being recognized by the immobilizer (anti-theft) system. If you have a second key, try starting the car with that. If you have push button start, hold the key up against the start button when you push it. If the security light stays on there is a problem with the immobilizer or key.
4. When you step on the brake, do the brake lights light up? If not, and your car requires you to step on the brake to start it, your problem is most likely in the brake pedal switch or associated wiring.
5. When you turn your key to on (not start) does your check engine light come on during the warning light bulb test? If not, your instrument cluster is probably not able to communicate with your engine computer. The cause could be a problem with the engine computer or with the data network. Check the fuses that supply power to your engine computer.
6. You can also check the fuses on the power feeds for other critical modules. That would include the body control model, transmission control module, and any other modules involved in starting the car, such as the immobilizer module and smart fuse box, if your car has those. A clue that the transmission control module is not communicating would be no indication of what gear you are in on the instrument panel. (There are other potential causes of that symptom, such as a bad transmission range switch.)
7. If your car has a plug in relay that controls the starter, you can swap it with another, non-critical relay of the same type. In most cars, the starter relay will be in a fuse box or dedicated relay box under the hood. If that fixes the problem, you most likely have a bad relay, although the cause could be a bad connection in the fuse box that you (probably temporarily) fixed when swapping the relays.
8. Tap on the starter while holding the key in the start position. If the engine turns over you have a dead spot in your starter and it will need to be replaced.
If you have a remote start on your car, especially an aftermarket one, those are a common cause of no crank and crank no start conditions. I can’t think of an easy way to test that, but it’s something to be aware of.