Help Nissan Altima 05 Won't start randomly?

[Cravinmoorhead]

Hey I recently purchased a Nissan Altima 05 SE several days ago. The car runs great I had oxygen and airflow sensors replaced along with brakes but it seemed to be working great. Then I drove to my friends house the next day, turned the car off, and when I came out it won't start. Nothing. The power will turn on but it wont attempt to start. I wait like 20 mins and then it starts. Whatever I think. Then several days later, I drive my mother to work early in the morning and stop to get food. When I want to leave the same problem occurs except this time it wont start even after hours. Triple A came and he jumpstarted it and I asked him if it was battery and he said he wasnt sure and that he had put it in neutral to start it (I dont understand all he did was jumpstart it?). My mechanic said the battery seems to be testing fine. Idk what to do anything it could possibly be that I should have my mechanic check up please let me know. Do you guys think that it could be some weird unfixable problem? Any suggestions please let me know Im worried I just got scammed for 9 grand. I got warranty on engine and transmission.

Also the lights AT check and service engine soon come on