You could try to repair the phone software using PC Companion..
Before repairing your device you may want to backup your information first. Check out this topic for more information on how to. How to backup?
If the issue should still remain I think that this needs to be examined and fixed at a repair center. For more information about how to submit your phone for repair and where, contact your local support team.
@wilkenas Please stop posting all around, Samuel has replied to your question. If you are not pleased,you can always contact sony directly. But as I have seen, you already did. This is a user support forum.
