Xperia Z keep rebooting topic

i'm kinda new to root.
i tried to root my phone earlier and it works, no problem at all.
then i try to flash Cyanogen.
i was unlocking bootloader with cmd.
it came to the step which was 'fastboot reboot', nothing happened.
the LED turned from blue to red, flashed a green one then black out.
i unplugge it then tried to turn on, vibrations and nothing happened.
i tried flashtool, with 'reboot device into system', my phone turn on then keep restarting when it reach the loading screen.
i tried flashing it, both C6602 and C6603(mine is C6603), didn't work.
please help, thank you.