3DS overheating plus screen won't turn on after repair

Hi. Ok let me start from the beginning. I've had an Old 3DS since 2018 but it was passed down to me by my cousin who bought it in 2011, I had to change the battery for the first time in 2023 and after that I modded it somewhat in december 2024. During the end of 2025's first semester it started to stop charging until it just stopped working in general, I took it to a repair guy who tried to change the charging port on my 3DS, we tried to use a different charger but nothing was working (batter shows no signs of inflation/getting bigger). Then he opened it up and discovered that apparently there was something wrong with the motherboard that was stopping the electricity from getting to the battery but if I take the battery out and charge it via an adapter it works. I came back home now (live in Brazil but was living for a few months on Italy) and tried to power it up, unfortunatly the blue LED turns on but both screens stay pitch black and won't even turn on. Also for some bs reason it's overheating on the left upper screen hinge when I power it on so I'm scared of leaving it on for a long time to see what happens. Can anyone please help me, this was my first ever eletronic/videogame and it matters a lot to me. Thanks