You can format your s60 phones in two ways.
» Soft Format :
On the main screen enter the code below.
Your default lock code is 12345 Also make sure your battery is atleast 75% full.
» Hard Format :
Hard Format can be done if your phone is facing any of
the problems mentioned below :
1. Blank screen. Phone unable to reboot.
2. Phone only able to boot-up to "Nokia" word screen.
3. Installed some program but not able to uninstall it after that.
4. Error messages such as "Child Installer" keeps popping-up.
Make sure cell battery is atleast 75% charged. If its not then you are putting your cell at risk. If its atleast 75% charged then do the following:
1. Switch off the phone.
2. Hold down the following three buttons: Green (call answer) button, * button, and '3' button.
3. While holding these buttons, press the power button and switch on the phone.
4. When the message 'Formatting' appears on the screen, release all of the buttons.
The procedure takes some minutes (approx. 3-4).
* Note: You shouldn't switch the phone off or remove the battery when performing either of these operations.