After latest update,phone doesn't turn on

[juventus]

I can't get into my xperia z3 after downloading the new update. I did it yesterday (24/7-15). It only says that Android is starting and that the phone is optimizing apps...after a while my phone doesn't work at all or just restarts again.

What is wrong? What can I do about it?

[Thommo]

Try performing a system repair using PC Companion as this will often fix issues - This will factory reset your phone and erase all data

Switch off your phone and unplug from Pc (Hold volume up and power for around 10 seconds)
Start PC Companion and select Support zone then Update my phone/tablet then in Blue Repair my phone/tablet and follow the on screen instructions - When prompted connect your phone still switched off holding volume down or back button - This should start the repair or reformat process

If you are using Windows 8/8.1 or a 64bit operating system then adjust the settings for PC Companion and run in compatibility mode and chose Windows 7 or XP