When you reformat your Xbox 360, all the data and information stored is deleted and cannot be recovered. So before you continue, make sure that you have backed up any required information on another device or you really don’t want the data on your device.
Before you start with the reformat, keep your Xbox serial number ready. Every Xbox is shipped with a unique 12 digit serial number. Make use of the Xbox Dashboard to get the serial number. Launch My Xbox and select System Settings, Console Settings and then System Info. Find the serial number displayed here. You may also find your device serial number by the back of your console, j ust above the A/V port or behind the oval USB door. Disconnect any connected USB devices and push the oval USB door to see the serial number. Serial number needs to be entered just before the reformat, this helps you prevent any accidental deletion/ formatting.
Now you can start your Xbox the disk tray empty. Now launch the My Xbox and select the System Settings and then Memory. Next you can highlight and select the device you would like to format. Press the Y button on your controller and chose Format. Your console will display the following message: This will delete all content on this device. Do you want to continue? Click Yes to continue with the reformat. To carry on further, you will be asked to enter in your console serial number. Provide the serial number and click Done. Wait patiently till your device completes the task.