When your smartphone is being unresponsive, sometimes the only solution is forcing it to power down. Shutting your phone off and turning it back on is known as a “soft reset;” it restores the phone to its initial startup configuration without compromising any of your user data. Think of a soft reset as the same process as restarting a computer. Since shutting down the HTC One usually involves having functional access to the screen, you need to soft reset it first.
Press and hold the “Power” button for around 10 seconds, and then wait for the phone to reboot. You'll be able to power it down once the operating system finishes booting.
Press and hold the “Power” button until the “Power Off” button appears on the screen.
Tap “Power Off” to shut down the phone.
The HTC One does not have a hard shutdown key combination. If the operating system remains unresponsive after a soft reset, you may need to bring the phone in for service.