Formatting a hard drive in DOS removes all data and restores the disk to its original factory state. It is important to make sure everything on the hard drive is copied to an external drive or storage device before formatting is done. Once a hard drive is formatted, all information is erased. After hard drive formatting is completed, the operating system is no longer available because formatting removes all software and is not reversible. Before you begin, make sure you are ready to start over again and that this is what you want to do.
Copy all of your hard drive's important data to an external storage device.
Click “Start,” “Accessories” and “Command Prompt” to enter the DOS prompt environment.
Enter the format command at the DOS command prompt. To format the C: drive using quick formatting, for example, type the following:
FORMAT C: /Q
If your hard drive is not drive C:, replace "C:" with the appropriate letter or your hard drive.
Press the “Enter” key and the drive is formatted section by section. When the formatting is complete, the drive is ready to be used again.