the black dot you describe, was it the pressure dimple which actuates the switch?
Hello there, I am having an issue with a iphone 4s. The power button was not working property but the phone was on. The power button had to be pressed really hard to get it to work. I disassembled the phone and realized that the power flex was missing the tiny black dot and made the outer power button difficult to reach it. I didn't have the flex to get it replaced so I assembled the phone back again but now it doen't turn on anyways. I connected to a charger, to the laptop and don't even the apple shows up. I noted that a screw and a little piece was missing at the top left side of the phone. I was wondering is that has something to do with no power on. Any of you have some ideas what may be causing this issue. If more info is needed please ask. Thanks for your help guys.