Hard Reset HTC One (E8)

First method:

1. Start by pressing the Power button to switch off the device.
2. Then press and hold Volum Down and Power button together for a couple of seconds.
3. Wait for the three Andoid images.
4. Choose the Factory Reset by pressing the Volum Down to navigate and Power button to select.
5. Success!

Second method:

1. If the display is off, press the Power button to turn it back on.
2. Go to Settings and then to Backup & Reset.
3. Tap Reset Phone. 
4. Choose Erase All Data if you are sure you want to clear all your data. 
5. Select OK to confirm the hard reset.
6. Success!

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.