Im under the assumption you have a modded xbox.
Make a disk with ConfigMagic on, by using an ISO tut
. You'll need this as you can't access the HDD. Make sure it is a medium your xbox recognises.
COLD boot the xbox by inserting the disk in the xbox, turning off then rebooting.
You should now see the ConfigMagic Screen. Use the recovery password option. It should be 'TEAMASSEMBLY' (as written without ' ' )
Your hdd drive should now be unlocked.