Just to be clear as to what the issue is. Your battery was drained and it would not start due to the alternator not charging the battery. So you changed the alternator but did you change the battery as well?
We should load test the battery at a parts store just to confirm it is ok. You just need to remove and take it in and they will test it for you.
https://www.2carpros.com/articles/car-battery-load-test
https://www.2carpros.com/articles/how-to-replace-a-car-battery
If the battery is fine then we need to start with this guide as to why it doesn't start:
https://youtu.be/dCjmRL3p4Cs
Please run through this info and let us know what questions you have. Thanks
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Friday, May 14th, 2021 AT 8:19 PM