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Make sure that you have the latest update on your phone:
http://www.sonymobile.com/global-en/tools/pc-companion/
Download and install PC Companion at your PC and connect your phone via USB-cable. PCC will then tell you if you have an update available.
Otherwise, I suggest that you boot your phone into safe mode to see if you experience the same behaviour:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008