Chosen Solution
My son uses an iphone 6s. He was using it yesterday and the screen went black. After that, we could not get it to power on. I have tried a hard reset, I tried to charge it overnight (it shows nothing when charging), and tried to connect it to itunes (it is not recognized there). Do you have any other suggestions before declaring it dead?
Check all connectors on the battery and screen and try measuring the current thats going into the phone and seeing if it takes a charge, if it does it’s likley the screen. If it doesnt take power try a new battery.