Thanks to reader “AJK” for pointing this one out. On S60 devices you could do a soft reset by pressing *#7370# , this should restore all settings to the default value and works without any problems on the 5800 XpressMusic. A hard reset reset deletes everything in phone memory and restores the phone to the  factory default status. On devices with a keypad, this was done by pressing the “Green Dial button”, “3” and “*” while the phone boots up. Due to the lack of these button on the 5800 XpressMusic during bootup, it made this key combination pretty much useless on this device. Making matters worse, the 5800 XpressMusic has User Data Preservation and there’s no way of overriding this.  The reason why I mention this is  installing/reinstalling the firmware via Nokia NSU has the same effect as a hard reset,  but the presence of UDP leaves everything intact.

Luckily there IS a hard reset code for the 5800 XpressMusic and it’s: pressing and holding the “Green Dial button”+ “Red End Call button” + Camera button while the device boots up. Just make sure backup before trying this one out.