In order to hard reset a Nokia 3108, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Nokia 3108 device will be brought back to the default configuration of a brand new device.
1. Switch on the device.
2. Go to Menu > Settings > Restore Factory Settings.
3. Type in security code (12345 by default).
4. Allow the device to reset and restart, completing the hard reset process. Voila.