santanu, you could try to reset your phone

http://en.kioskea.net/faq/470-how-to-res...

1. *#7780# - Restore factory settings - resets all the settings to the default ( you will not lose any data)

Make sure you back up your data as you will lose all of it when you perform option 2 or 3 on this list. The default code for ALL operations listed here is 12345

2. *#7370# - Reformat your phone (out of the box, tho keep in mind that most newer nokia phones at least n series, e series and s60 based phones have udp - user data preservation so not ALL data may be lost. still it is a good idea to always do a back up of your stuff.)

3. This you perform as a last resort. Nothing else is working.If the phone is not showing any activity, proceed with hard formatting , turn off your phone, hold the following buttons while pressing the power button. (the default code is 12345)

hard reset - hold the following buttons *, 3 (number button) and talk/green key. turn on the phone and do not release those buttons until you see the Nokia boot up screen. once you feel the phone power up you can let go off the power button while still holding all three buttons

http://discussions.europe.nokia.com/t5/O...

If none of this works you can also try to update your firmware. Download and install the latest Nokia Software Update and Nokia PC Suite, connect your phone, and run NSU. You will be prompted to update the firmware if a new version is available. Just make sure that you backup your phone since it will delete everything in th memory of your phone.

And if none of that works, you should definitely contact your cell service provider. Did you pay your bill :-)? Good Luck to you and let us know how it is going.