samaviak i doubt it to be a hardware problem
Give software repair a try and see if it solves the problem
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Backup everything as it will erase all data on phone (sms, contacts,apps)
Update/Repair your phone via PCC or SUS
PCC (PC COMPANION) – Repair your software with this .First do the setup without connecting your mobile to pc.(only connect when you are asked to).
Do it as follow >> PCC > SUPPORT ZONE> SOFTWARE UPDATE> REPAIR SOFTWARE (written with blue)
PC Companion http://www.sonymobile.com/global-en/tools/pc-companion/
SUS ( Sony Update Service) ... download and install it on pc and follow the on-screen instructions
http://www.sonymobile.com/global-en/tools/update-service/
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If this doesn't help, you will have to get it examined at the service center
