How to Wipe Your Computer Without a Disk
Wiping clean the contents of your home computer is a drastic but required step in many cases. Your computer may be infected with a radical virus or numerous malware infestations, or you may simply wish to dispose of the computer without your personal information on the hard drive. Absent a disk, you will be able to clear only the non-bootable sections of your computer's drive.
Right-click "Start," and choose "Explore."
Right-click the system drive that you wish to wipe.
Select your desired file system from the drop-down menu and press "Start."