In order to hard reset a Nokia 8810, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Nokia 8810 device will be brought back to the default configuration of a brand new device.
1. Turn on the phone by holding down the Power button.
2. Open the Dialer and type in the 1809#*101# or 2945#*101# code.
3. Press Call button to confirm the process.
4. Voila! Phone will now reset and restart, thus completing the hard reset.