I had this prob w my Note4. Came close to junking it. I did everything from putting it in the freezer for 20 mins, to setting it in the sun, to doing nothing for a few days, to trying different cables, to doing a recovery boot, to safe mode, to power button hits, to buying a new battery.
I am NOT a tech whiz. I understand little about my phone. I’m a woman in my mid-50s. But I'm a stubborn problem solver and look for online fixes to probs w electronics.
Here's what's working for me—though it's not a perfect solution. I'm continuing to pursue a complete fix.
My phone was completely dead and wouldn't take a charge. Just vibrated and buzzed. Just before that, it randomly shut off and on. It was really rainy for a few days, and I was outside w my phone. That prob was an initial problem. But even 2 weeks after the rain incidents, the phone wouldn't work. I was really quite hopeless about it reviving.
My #1 suggestion is to try to charge up the phone via a computer and USB cable. The low battery (around 15%) is problematic. I found great hope in knowing that if all else failed, I cld charge via a computer.
Once the phone took that charge, I did a factory reset. It now will charge from AC, but seems very finicky about which charger and charging cord it will work with. So far, I haven’t been able to get it to charge w a car charger. Still working on that.
I'm also charging up the other 2 batteries I have for this phone in case I get caught w a really low battery again and no place to charge. Work in progress . . .
Hope this helps someone.