How to hard reset Windows Phone 8

You will lose all data on the phone, you are warned!

1. Power off the phone. 
2. Press and hold Volume down key while connect the charger to phone. You will see a big exclamation mark on the screen. 
3. Now press these keys in sequence: Volume Up, Volume Down, Power, Volume Down. 
4. Phone will reboot and you will see rolling gears on the screen, it will take couple minutes to fully boot up. 
5. Your phone is reset to factory settings and just like a brand new phone.