Shutting down itself in start

[Carrotty]

Hi I bought a mobile for about 7 months ago. It has started to reboot all the time now so I can´t do anything, only have time to get into the home screen then it restarts again. This started just after a system restore and after I downloaded three apps on mobile. Fb Messenger, Snapchat and Instagram. It has since before, rebooting itself suddenly several times. And had major problems calling then phone died in the middle of the call, even then restarted itself. Have read a bit on the forum but can not find a similar problem with the phone constantly reboots itself so I can´t  do anything about it. Have tried to load it in the socket and in the USB on the computer, but nothing works. It loads properly. Usually get just to click settings then it restarts again. All the time. Now it has done so in 3 days.
What is wrong? I can do anything or is it completely broken?

[_alexdon_]

Did you try another SIM in your device?

[Alexander1]

If the behavior persists with another SIM card I suggest that you try to repair the phone software using PC Companion: 

http://www.sonymobile.com/update

In PC Companion, press start on Support Zone > Start on Update the phone/tablet software > click on the blue highlight (Repair my phne/tablet). Do this without the phone connected. Follow the instructions on screen to perform the repair.