You could always try to repair the phone software using PC Companion:
http://www.sonymobile.com/update
In PC Companion, press start on Support Zone > Start on Update the phones software > "Repair phone".
However, it sounds like you need to have your phone examined by a service center. Please contact your local support team for more information:
http://www.sonymobile.com/global-en/support/contact-us/
