hey everybody

i just found the solution for the topic.
1. install the flashtool
2. after install the flashtool, open cmd in administrator then type "bcdedit /set testsigning on" and then restart your pc
3. after pc your restart install the flashtool driver at "C:\Flashtool\drivers\Flashtool-drivers.exe" and select "flashtool driver & fastboot driver"
NOTED : when the installation process there will popup window warning just Click "install the software anyway"
4. after complete the installation, open the cmd in administrator again and type "bcdedit /set testsigning off" and don't forget to restart again your pc.
6. after restart your pc open the command promt at fastboot folder then type "fastboot devices" and you will see the list of devices in fastboot.
If not, you missing some steps. gudluck. I already done flashing my Xperia Z 4.4.2( Kitkat ) to 5.0 ( Lolipop )