In order to hard reset a Samsung E810, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Samsung E810 device will be brought back to the default configuration of a brand new device.
1. First of all, press-hold the Power button.
2. Enter the *2767*3855# code into the phone. Press Call button to confirm.
3. Wait for your device to reset & restart. That is all.