Formatting a Xbox 360 HDD is very simple but can turn to total disaster if done wrong!
So in this instructable I will show you how to format a Xbox 360 HDD
*Note* This instructable only covers the new NXE from Microsoft
Step 1: Start Up Your Xbox 360
So first start up your Xbox 360 then when you get to your NXE dashboard go under "My Xbox" and scroll to the right until you hit "System Settings"
Step 2: Back Up the HDD
At this point you will want to Back Up the HDD!!!
To do this grab a flash drive larger than 1GB and plug it into any USB port on the console and go to "Memory" in "System Settings" and select the Flash Drive and configure... This may take 15 seconds or more. Next go to your HDD and move stuff over to the Flash Drive. There is another way to transfer files is by buy a transfer cable from Microsoft and transfer files over to your PC!
Step 3: Now Format the HDD
*Note* This will take awhile depending on HDD space or how much is stored on the Drive!
You will get asked to enter in your Xbox 360 serial!
Step 4: Your Done!
Now go enjoy yourself as now you have a formatted drive! :D