you probably locked it with the wrong key. ive done it several times. Unlock the hdd with atapwd using the master password XBOXSCENE and then try locking it again. Oh and if you are trying to use the key that was in the txt file from your eeprom backup, its not going to be the correct one for your new drive. you need to boot your pc into windows with your new xbox drive unlocked and hooked up to one of your ide cables. then open a program called liveinfo and load your eeprom file then select the new xbox drive from the drop down list. it will tell you the correct key for that HDD and your xbox. its time consuming, but thats how it's done.