In order to hard reset a Nokia 7710, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Nokia 7710 device will be brought back to the default configuration of a brand new device.
1. Turn off the phone.
2. Turn it back on. Upon seeing a Nokia logo on-screen, press [= and Menu buttons.
3. Few seconds after press and hold the below button.
4. Select what you want to format. Confirm.
5. Your phone should now reset and restart. Well done.