I'm not sure that i understand the problem correctly but if you have problems with the phone restarting itself or it doesn't turn on you can try to repair the software in the phone using PC Companion.
First download and install PC Companion if you don't have it in your PC:
http://www.sonymobile.com/global-en/tools/pc-companion/.
Then start PC Companion without the phone connected, select "Support zone", "Start" for software update and then "Repair" and follow the instructions from the software.
Please note that all data in the phone is deleted when you do this.
