I bricked my sony xperia mini pro over a dozen times and still managed to get it on track using this method.
01) download the xperia flash tool https://unrestrict.li/flashtool
02) download the latest firmware for your device from the sony support page.
03) install the flashtool then goto the installed directory... find the firmware folder and copy the downloaded firmware file into it.
04)start the flashtool.... switch off your phone..... give it about 10 seconds... then hold the volume down button and plug it to the PC.
05)The flashtool will detect the phone... then click on the lightning bolt sign in the flashtool...select flashmode -> ok
06)then select the frimware for your phone in the next window....
07) Then press flash...
thats it. The flashtool will flash the stock firmware and the phone should be unbricked.
hope this helps.