If there is no critial data on the drive, use the control panel to remove all of the programs which have nothing to do with the hardware function.  Often you can use an internet search engine to help sort out what is best to leave.  Make sure that you delete any games.  Use Explorer to delete any directories for the games and programs removed.\n\nNext delete all of the files from My Documents.\nNow you need to run a utility called Disk Cleanup.  This will depend upon which version of Windows you have, but you should be able to find it using the Help function (It is usually found in Programs, under Accessories, System Tools).  Delete every thing that you can, including the stuff in the Trash can.\n\nNext open My Computer and highlight and select your hard drive with a single right click.  You should see an options window open.  Left click on Properties to open a drive window.  Next left click on the Tools tab, followed by the Defragment button.\n\nOnce the Defrag is done, your drive is going to be as clean as you can get it without special programs or information.  Windows should not be affected.
I am selling a computer, what is the best way to clear everything from the hard drive?