A hard drive is the brain of a computer. However, over time, that brain can become overworked and overly saturated with old software and outdated information. It becomes clogged and needs a fresh start. By erasing a hard drive, you can give your PC that fresh new beginning. With a few steps you can erase your hard drive manually, without the aid of expensive software.
Make sure your data is protected before you proceed. Whatever you do not save will be lost once you erase the drive. Use a CD or jumpdrive to save your information. Boot with a system disk. Before you continue to erase the hard drive, use the system to create a system disk. Use a 3-1/2 inch floppy disk and format it with the command "format a: /s"; this will create a bootable disk that contains system commands. Place it in the drive of your system and turn it off, then back on. Reformat the hard drive. Once you've booted with the system disk, type "format c: /s"; this will reformat the hard disk, virtually destroying the old hard drive you used to know. Depending on the of the drive, the formatting may take a fairly long time. Once the formatting is over, use the command "fdisk" to create partitions (which are logical sections for your hard drive's storage). Given the newer hard drives and operating systems of today, you can fdisk the drive and use all of the space. or if you dont have a floppy drive Download a disk wiping utility, such as Darik's Boot and Nuke (DBAN) or KillDisk. DBAN is an open-source product, while KillDisk is available as a free, closed-source download. http://www.dban.org/ http://www.killdisk.com/
Once you download the file, save it to your computer somewhere easy to remember. Insert a blank CD into your computer and use a CD writing program to burn the hard disk wipe utility to the blank CD. If you are using Windows Vista or 7, there is a built-in utility that will perform this task. Back up the data on your computer that you want to save, if necessary. Insert the CD that you created into the computer that is attached to the hard drive you wish to erase. Power on the computer and choose the setup option to boot from the CD. Once you have booted from the CD, you will enter into the hard disk wipe utility. Depending on which utility you chose to use, this screen will vary, but the choice you want to select is to erase or wipe a disk drive. Choose the hard disk that you wish to wipe and confirm that you wish to permanently erase the data on it. Before confirming this, you may wish to physically double check and ensure that you are erasing the correct drive. Once you start the erasing process, it cannot be halted, paused or reversed. You will have to wait for anywhere from a few hours to even a few days for the process to complete, depending on how large your hard drive is.
or you could just reinstall another operating system this will automatically delete the old wrong one you installed.
Hope this helps.