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I suggest that download Update Service to your PC:
http://www.sonymobile.com/global-en/tools/update-service/
Install Update Service and follow the instruction until you get to the step where you are asked to connect the phone. Connect the phone via USB-cable > When the phone is connected, hold down the volume down(-) button > At the same time you hold the volume down button, you also need to hold the force OFF button down. Hold the force OFF button down for a longer time (5-10 seconds) and do not release the volume down button. Hopefully, you can perform a software repair on your unit.
