Please answer my question first: Which firmware version do you have? Check by pressing *#0000#
Edit: Someone with
the same problem and same phone fixed the problem by doing a hard reset. Are you sure you did it correctly? Try
this "3-finger solute" method too.
Edit2: On the
Nokia Support Forums they found no solution, you have to go to your nearest Nokia Service Centre. You don't need to pay them anything, just get them to look at it.