There are times when you have used your symbian phones to an extent where some incompatible applications or viral infections begin affecting the performance of your mobile. All you need do in this type of situation is to Hard reset your phone to optimise its speed and performance. There are two aspects or types of reset i would touch in this post.

Soft Reset:

To soft reset your symbian phone, you need to know the security code of the phone. After you boot your phone, you then type in *#7370#, your security code would be asked of you by the phone, type it in and press OK. The phone would restart and all those problems would be solved on your phone. If they persist then try the HARD RESET below.

Hard Reset:

In this case, all you need do is switch off your phone and then hold this four keys at the same time, starting like this

* + 3 + Send Button (Green key) + Power button.

Note that in s60v2 (though not all), the word formatting can be displayed while s60v3 don't display them. Make sure that your phone asks you to reset time, date and other stuff. If you didn't recieve such a prompt, it means you didn't hold the buttons properly, so you have to redo it to achieve your Hard Reset. Drop your comments please.

Other Method

Few days back i tried to reset my Nokia N78 but i failed, the above method did't work on my Nokia N78, but it worked on N73. So i found a new way to reset my N78.
its same as above method, i just modified it little bit.

* + 3 + Send Button (multimedia key) + Power button.