Bootloader must be unlocked if you need to boot custom Recovery or ROM,If your bootloader is not unlocked properly then USB logo will appear..So use this Tool to Unlock the Bootloader in Correct Manner
Extract using the password :
Find .exe file inside the Extracted folder and Run it to Unlock/Relock the Bootloader…“Don’t Relock after you flashed img files..”Relock only when you need to flash Stock Firmware…..!!!!!!
CHECK OUT MY APP FOR ZENFONES- http://tecky-world.com/2015/09/20/new-zenbox-toolbox-for-zenfones-root-v1-0-5/