My car will not go into drive at all. Why is this happening?

Even though the link below is written for Hondas, the basic information is likely applicable to your situation and should give you better insight into your problem:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-3.html#post258005

I would focus on a faulty automatic transmission gear position switch.