In case of Nokia E7, there are two ways of hard reseting the phone.
1) go to Dial Pad and enter *#7370#. You may be asked to turn off data services for which you can take the phone offline and retype the code to erase everything off the phone .
2) For extreme hard reset where the phone is not going to the dialer and nothing is responding there is a three button procedure.
Press the Menu Key , Down Volume Key and Camera Key together and press the Power button on the top till the phone vibrates , restarts and goes to Connecting People Logo.
Its done