In case you need to hard reset Nokia N8 phone due to various reasons, here are the steps you need to follow:

1) Select call and type in *#7730#
2) Press the power key and select Offile Profile
3) Call again to *#7730#
4) Confirm Hard Reset

This will remove all the information you have stored on your memory (internal memory and 16 GB memory). The N8 Soft Reset operation can take up to few minutes depending the amount of information you have installed on your cards.

Here is an alternative way to master reset the phone