In order to hard reset a Nokia Lumia 710, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Nokia Lumia 710 device will be brought back to the default configuration of a brand new device.
1. Turn off the phone.
2. Press & hold the Power Down + Camera + Volume buttons simultaneously.
3. Let go of the Power button when the phone vibrates. Hold others until the phone restarts.
4. Voila, done.