since you are at the step of locking the drive, which means you have already install every xbox require files for the replacement hard-drive to be like the exact same as the originals xbox hdd, then why don't you try and put it in your xbox to see if it booted up? if you can get it to boot up, use the evox backup option to find out your password...
and that's why you should use this UnlockX program instaed of the hddpreper or something becuase UnlockX save the locking password number that you enter...
but this tutorials is really long and hard, it is surely not for newbies

s... I have just follow what this tutorials said but i use unlockx instead of the hddpreper and it works fine...