Samsung C6620 hard reset with buttons / keys
With the C6620 turned off, press VOLUME UP + 4 way pad UP + POWER ON. Password: 0000

OR
Use this method to hard reset your Samsung C6620 phone: Enter *2767*3855#. Warning! All your data including contacts, messages etc. will be lost! Copy all your necessary data/Contacts/Messages etc. to SIM or make backup to your PC before full reset! Take out SIM card before full reset.