Whether you want to reinstall Windows XP cleanly or start off fresh with a new operating system, it is sometimes necessary or preferable to format your hard drive. Formatting a hard drive erases all data and prepares the drive for a particular type of file system. Although newer operating systems such as Windows XP and Windows 7 allow the option to format from within the operating system, formatting also can be accomplished from the command prompt.
Back up the data that is on the hard drive you want to format. Reformatting your hard drive will remove all of the data on the hard drive, so back up anything you want to keep.
Click "Start" and click "Run." This will open the Run dialogue box.
Type "cmd" in the text field and press "Enter" or click "OK." This will open the command prompt.
Type "format c:" into the command prompt and press "Enter." The computer will begin to format the hard drive.
Type "format /?" at the command prompt to see a list of formatting options.
Only format your hard drive if you are sure you are comfortable removing all the data. Reformatting will remove all data on the hard drive. Only format a hard drive if you have a system restore disc so that you can install the operating system.