Nokia 5250 hard reset
You can format your device by typing *#7370# in standby mode. Before the device is reset, you need to provide the lock code. The default lock code is 12345.
Some Nokia phone can be reset via this menu option
Press menu button or enter Menu > Settings > Phone > Phone management > Factory settings > Delete data and restore > YES
Formatting the device will permanently erase all user data and settings as well as add-on applications and operator specific settings.