Instructions
Turn on your XBox 360, remove any discs from the tray (if applicable), and then navigate to "My XBox," "System Settings," and click "Memory."
Select your hard drive from the list of storage devices, and then press the "Y" button on your controller to view the Device Options menu.
Click "Format," and select "Yes" to reformat your hard drive. If prompted, type in your system&'s serial number (on a sticker on the back side of the console) and click "Done." Your XBox 360 hard drive will now be wiped.