Although using a Windows installation disc helps speed up the reformatting process, it is not ultimately necessary. The first step you should take is to backup all your essential data and save it on an external hard drive or on CDs/DVDs. This is because the formatting process presupposes wiping all information from your hard-disk. Next, it is necessary to remove from your system the hard drive designated to be formatted. If you do not, you would find that it is almost impossible to carry out the formatting process for the primary partition (that is the one which the operating system is running on), while your PC is still functioning. Afterward, you should use an external USB case, in order to attach the hard drive that will be formatted in the likeness of an external drive. Then, you should access the "Disk Management" section in your system's "Control Panel." Finally, you may pick out the designated hard drive and select the "Format partition" option in order to complete the process.