You will probably have to use Recovery Mode as described here. You may have to try to enter Recovery Mode more than once to succeed.
I want to know how to reset my iPhone without unlocking it because I've forgotten my password and iTunes isn't recognising my device and says error
User profile for user: ss.03
Question: I want to reset my iPhone but I forgot my password and I've downloaded iTunes but it says error eveytime I put the USB cord in?