I've did a Google search on rooting your phone and have realized that all the available methods suggest the user to first unlock the bootloader and later root it.
Maybe Sony has put some barrier to prevent these kind of situations or maybe this is a failed factory reset. Hence, I suggest you reboot the phone into fastboot mode and do a factory reset.
Steps:
- Download the appropriate USB drivers for your device.
- Download the slim version of ADB and Fastboot. You can find this in forums.xda-developers.com.
- Install the USB drivers for your device.
- Now, search Google on HOW TO BOOT your device in fastboot mode or bootloader mode.
Note: There is a way to boot the device into fastboot mode directly but since your phone reboots every 25-30 seconds, this cannot be possible.
- After you reboot to fastboot mode, goto
Start
> Run
and type cmd
- Extract the previously downloaded adb and fastboot and type
cd c:\path\to\adb\directory
- Type fastboot devices. Note: fastboot and adb require Administrator privileges to work in Windows 8 or later.
- Now if you can see a device besides a blank input, then you have installed the USB drivers correctly.
- Now, type
fastboot erase userdata
and fastboot erase cache
.
- Now reboot by typing
fastboot reboot
and wait.
With a little luck, your device might boot.