Set up your BIOS. There is really only one way to format a hard drive, and it's through some kind of bootable device. If it isn’t the Windows CD, it can be an external drive or another CD. When the computer starts up, it will tell you to hit a function key to enter the BIOS; you must quickly hit whichever key is indicated. Once you are in the BIOS, search through the menus until you get to an option that reads something like "Boot Device Order." Select "CD-ROM," "Removable Device" or something similar, depending on what kind of bootable device you will use. Exit and save your changes.
Make a bootable disk. You need to download the files from somewhere to make your bootable device. The Bootdisk website has a good selection of files; some are free and some are not. For a CD, you must have CD-burning software. You will need to run the software to copy the files you have downloaded and select “Make This CD Bootable.” In making the bootable device, make sure one of the utilities you download has a format tool.
Restart your computer. Start the computer with the BIOS correctly set and the bootable disk in place. The computer will run from the boot disk or boot CD. If you are using standard DOS on your boot disk, you will just need to type “format C:” ("C" refers to your hard drive). If you are using another program, you will need to use its commands.