Here is how to hard reset ( back to factory default settings ) Nokia Express Music 5800.

I suggest you back up your phone content using Nokia suite before proceeding because hard reset will erase everything from your phone. If you have a memory card I suggest you backup the contents and then format it because some of the apps you downloaded trough Ovi Store are actually installed on your memory card and the next time you attach the memory card after hard reset those apps will be installed again.

To hard reset your phone using on screen keypad enter the following code:

*#7370#

Then for security code enter:

12345

Your phone will restart and after some time booting will be as good as new!