In order to hard reset a NEC 804N, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
NEC 804N device will be brought back to the default configuration of a brand new device.
1. First, press-hold the Power button until the phone turns on.
2. Now press the Menu button.
3. Open Settings Menu and Reset Settings and type in security code (1234 or 0000 or 000000 by default, possibly).
4. Confirm the hard reset operation. Voila, done.