Samsung galaxy GT-P6200 completely dead (long explanation please help)

So my samsung galaxy GT-P6200 is completely dead, I tried all the key combination ex: power+volume up/down many many times, still doesn't work.

I was on the bus listening to a song, when the song finishes I wait for another song to play since it's on a playlist but I hear nothing, so I try to unlock my phone by pressing the power button and nothing happens, so I keep on trying and decided to stop after awhile because it doesn't work and just gonna do it at home, so I did.

So his kinda happened before and all I did was to wait until the battery ran out by itself and then charge it, so I thought it will work, and it doesn't so I kept on trying all the key button solution and nothing work, I tried to plug it to my computer nothing work. And so I decided to bring it to the Samsung Service Center and the said they have to open it up to see what happens and by oding so it will ruin my screen since my screen is in bits and pieces only being held by my screen protector so I will have to replace my screen and it cost a lot and they also out of stock for it since it's an old type. So I said thank you and went out since even if they have the stock I won't be able to afford it, it'll cost almost like buying a new phone.

So I went home check out more tutorials and Solutions from google and I kept on thinking that maybe if I do it myself I would be able to open it just fine with more care to it than the lady at the service center, so I search about how to open it and I did it! I open the back completely with just a few tiny scratches at the sides not completely ruining the screen like the lady said. And so I tried to unplug the battery for about 30 minutes and then pug it on again and then charge, doesn't work.

And while charging I noticed that the thing I assumed the motherboard become warm and so I thought it's not completely dead then. So I thought maybe the battery works but the motherboard just doesn't start up so after awhile now I left it with my dad's friend and he have no idea. I just got it back and it still does that motherboard become warm thing but then I realized that the batter is cold, maybe I have been thingking it wrong the whole time and it's not the motherboard that doesn't respond but it's the battery.

But I don't know, don't the electricity went to the battery first the to the motherboard? So I thought that the battery did fine delivering the electricity to the motherboard but it just doesn't respond. I haven't put the back on again since, if I put it on again I won't be able to open it for the second time affraid I might actually broke it trying to open it.

I need help to make his phone alive again! I can't afford another phone, so did my family! And I really don't want them to spend more money on a phone for me when they can use it for more important things and I have a lot of important things on it that I just can't lose!

So Please! Please help me! If you read all that thank you so much! And I hope if you know something help me, if you know a friend or a family please do ask them, I kindly ask, it will meant the world to me! Please and thank you first and foremost for reading and please pray for me so that I can find the answer and fix my phone completely.

Thank you have a great day!