Thanks all so so much for the great solutions. Just want to share what I did after 3 hours non-stop trying and finally fixed my Samsung Nexus power button issue. Hope it could give some ideas to those who still have this problem.
1) Connect phone with USB cable to the computer
2) Take out battery
3) Press the volume down and power button at the same time AND put battery back in
4) keep USB cable plugged
5) phone charging and battery status will flash on screen for multiple times; keep USB cable plugged
6) keep pressing the Volume down button AND power button together for about 10 seconds, the phone finally powered on.
Repeat steps 1) to 6) for several times if needed. It took me multiple times to finally power on my phone.
Once my phone is powered on, I immediately download the app “Volume Unlock Power Button Fix” from Google Playstore to be able to turn on/off screen without power button. This app is the easiest one to use after I tried several other apps:
- turn off screen by pulling the app from notification bar and click “Turn off screen”. You need run the app and place the app on notification bar which is easy.
- turn on screen by using the volume buttons.
So now, you don't need the power button to turn the screen on/off.
The other nice app to turn off screen easily is called “switchoff” which allows to switch off the screen by pressing the app (placed on home screen) without pressing the power button. But I could not figure out a way to turn on the screen with same app.
Best of the luck!