Instructions
Start your Xbox 360.
Remove any disc that is in the system.
Select "My Xbox" and then "System Settings."
Highlight the hard drive.
Press "Y" to open the "Device Options."
Choose "Format."
Confirm that you want to format the hard drive by selecting "Yes." All information on the drive will be deleted.
Enter the serial number of you Xbox system. The serial number is located above the USB ports on the front or under the Ethernet port on the back of the system.
Select "Done" to finish the formatting.