Sony Xperia Z1 won't start up again!
Try to re-install ROM on your device (here's the newest firmware), that usually helps in similar situations. 

If your phone will be still broken that means you have damaged bootloader (boot partition) - then try to re-install boot partition (you can find instructions in internet).

At most you can give your phone to service and tell that your phone has been broken during an update. Repair will be free if you have warranty.