First method:
- First of all, switch off the mobile phone by holding the Power key for a few seconds.
- Then press and hold together Volume Down and Power button.
- When you feel the vibration, immediately release the Power key and keep holding the Volume Down button.
- You can release this button when you see a large exclamation mark.
- In this step press the following sequence of buttons: Volume Up - > Volume Down - > Power - > Volume Down.
- Good job! Tha hard reset has just been performed.
Second method:
- If the display is off, press the Power to turn it back on.
- Go to Windows Phone Settings.
- Afterwards select About.
- To confirm the whole operation tap Reset your phone.
- Well done! It may take a while to finish the hard reset.