My phone doesn't turn on-why?

I put my phone on charge last night and today morning it doesn't turn on. I gave it to some IT people to my neighbourhood and they said that the charging port is fine and they tried to hard reset it and because it didn't respond in any way they told me that it is probably a problem with the motherboard. However, I didn't do anything to the phone. I was wondering if the battery is completely out of charge due to it being faulty (but not exploded-because we checked it and it seems fine from the outside), would the phone hard reset?

In other words, is there a way to check if it is a battery or a motherboard problem that my phone doesn't turn on?

Thank you for your help.

P.S. My phone is a Samsung Galaxy J7 (2016)

Welcome to Android Central! It looks like that phone has a user-removable battery -- the easiest way to test would be to try a new or different battery.

How did your IT friend determine that the charging port is ok if it won't even turn on?