Try starting up the phone in safe mode to see if the problem is due to native firmware or is due to the installed third party apps. If it works properly in safe mode, then the problem is probably due to third party apps. In that case you will have to uninstall any recently installed third party app. To use phone in safe mode, do this: switch off the phone--switch it on--after the Sony logo appears, tap menu button intermittently--your phone will boot into safe mode diabling all third party installed apps, and there will a watermark saying 'Safe mode' at the bottom of the screen.
