Check to see if the phone is in standby mode.
To begin, hit the POWER button to see if the phone is indeed turned off. The phone did not power off if the screen quickly returns to the same screen as before. It is usual for the screen to turn off after a specific amount of time. In Settings > Display & gestures, Display, gestures & buttons, or Display, you can change how long the screen stays on.
Update the software on your phone.
If the problem isn't caused by an app, check for software updates on your phone and, if one is available, download and install it.
- Go to the Settings menu.
- Select About > Software Updates or Software Updates from the drop-down menu.
- Now press the Check button.
