Why won't my power button work? --> HTC One M8

[AC Question]

I have an HTC One M8, just sent to me from AT&T in exchange for an HTC One M8 that had several connectivity issues. This new one will send texts and calls and connect just fine, but the power button only works to take screenshots. If I try to push it to make my screen go black, it doesn't work. I also have a Dot case, so I keep looking at my phone and the dot wallpaper is always on, and I can't do anything to turn it off... so I'm afraid this is draining battery life unnecessarily. Has this happened to anyone? Does anyone have an idea of what might be wrong?

 

[B. Diddy]

Welcome to Android Central! So the Dot View is always on, even when the cover is open? What happens if you remove the case completely?

Make sure there isn't anything right by the phone that could be causing an electromagnetic field--any magnet could trigger the Dot View (which is how the case itself works). If the Dot View persists even without the case and with nothing magnetic nearby, the phone's Dot View/smartcover sensor might be faulty.