It might be worth you trying to do the following reset:
Enter into your keypad *#7780# and when prompted, enter the default passcode 12345. If you have changed the code, it will be the code you changed it to. A backup will not be needed as this will not delete any data.
Also, you could download Nokia Suite and check if there is an update for your phone, which in essence may be that your software is outdated.
Hope this helps and let us know how you get on.