Screen won't turn on

So I have literally done everything, I've checked the battery the battery works, I've cleaned all the ribbon cables to make sure, I've disassembled it and everything nothing has corrosion on it everything is great and I cannot figure out why it won't turn on. There's absolutely no damage on the motherboard whatsoever or any other part of the internals for that matter. There's no visible cracks on the screen or inside of the system. I don't think there's a problem with the charging port because I will plug it in and it will heat up the battery as if it's charging. I also tested the battery to make sure that the battery works the battery works fine. I also plugged it into the computer and the computer recognize that something was plugged in but it didn't pull up anything/ it didn't pull up the switch as if it was on. There is no responsiveness from the screen whatsoever I'm also not getting sound I cannot figure out what to do.