Xperia Z1 reboots automatically after coming out of lock screen?

[prateekj]

I am using the latest 4.3 firmware update. Sometimes after pressing the power button to enter the lock screen and swiping the screen to unlock, it shows the Xperia logo and then the Sony logo and the phone starts booting. I thought from some previous answers that it is due to 3rd party apps and I removed them from my phone keeping only trusted apps from Playstore. The problem still persists and it has begun to happen 3-4 times every day which is very annoying. Is this a problem with the power button that while unlocking it causes the phone to reboot or any another issue? 

WHAT SHOULD I DO 

PLEASE HELP ME.

[_alexdon_]

Try a force restart(power button+vol up until the phone vibrates).If the event occurs after,repair with sony update service).

[prateekj]

Thanks for replying. But I am unable to figure out which model to be chosen in Sony Update Service. My model is C6902 but in Sony Update Service it says SO-02f, SO-01f, SOL23, C6916. How do I know which one to choose and before repairing what backup is essential?

[_alexdon_]

C6916.