It could be due to third party app interfering
Check apps such as antivirus, task killers ( same types ) and revise their settings
Explore these threads of similar type
3G Data traffic keeps switching back on
My Xperia X8 display light automatically turns on, even if not in use
XPERIA S, wifi auto switch-on
Display keeps turning on.
Fail to Save Default Actions
Screen Blinks every 10 secs after locking in Xperia Neo V
Display keep turning on/off automatically
Live with Walkman screen turns on suddenly
If they don't help then repair your phone
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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-support-downloads.sonymobile.com/Software%20Downloads/Update_Service_Setup-2.11.12.5.exe
or
http://www.sonymobile.com/global-en/tools/update-service/
Both the links are same
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