- Turn off your phone.
- Hold "Volume Down + Camera Key + Menu Key" and press power button until your phone vibrates.
- Keep the keys pressed until the phone asked you to enter the needed details and welcome back ;)
P.S. Do remember that it will remove all your personal data too. That means data from C drive i.e. contacts - messages - bookmarks etc so you better take a backup first.
It's known that after hard resetting your N8 will create a problem for installing Nokia Store. Some users reported that installing the latest Nokia Store based on qt sorted out this problem however if that didn't help, install it through this file and you will get the earlier version installed and then you can upgrade to the latest one. Process is in the archive file already.