Turn off him self

[Atmac1953]

My xperia C6903 turn off him self. He goes out automaticly. Already I have reinstalled the software and the problem persists. In order that it could work I have it on freeze ice substitute's bags. What I must do.

[Uliwooly]

Remove both the MICRO SIM card and SD card > check if the phone reboots, if it doesn't then it could be a faulty SIM card, or if you trimmed the SIM card that could be the issue too 

[Uliwooly]

If the above doesn't help then you could boot on safe mode, if the problem stops then its an app acting up 

http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008

If the problem persist then repair your phone with PCC

PC Companion (PCC)

Bridge (for Mac)

Alternatives on How to backup Xperias

http://talk.sonymobile.com/thread/36355