Source: http://discussions.europe.nokia.com/discussions/board/message?board.id=smartphones&thread.id=61015
If you still experience problems, you can try if formatting your Nseries device helps. Format your device by dialling *#7370#. The device will request a security code, the default code is 12345 unless you have changed it.
Note that formatting will delete all user data from the device memory so always make a back-up to a memory card or use Nokia PC Suite.
If you think your Nokia device needs repair, go to www.europe.nokia.com/repair to find authorized Nokia Care Points globally.
*#7930#
USE AT YOUR OWN RISK!
I am not responsible for the damage caused by this command, to you and/or your cellphone.
Source: http://forum.brighthand.com/showthread.php?t=230485
*#7370#