This is the only thing I would try without taking to a service center.
Phone needs to be on. While phone is on, pull battery from phone. Replace battery. Power phone on. It should say: Please enter special code. Enter a string of 0's (usually 6 of them).
Unless your phone says PIN Blocked call customer care at 1-80-639-6111. In that case, a proprietary unblock code must be provided by a customer care rep.
Hope that helps!