Clear All Files from a Computer Running Windows XP

Wiping all files from a computer's disk would effectively render it useless, but it is possible to delete most or all nonessential files.

Steps

Back up all of the files that you need, probably onto CDs or an external hard drive.
Navigate to "My Computer" on the start menu, and right click on the drive that you want to delete the files from.
On the drop down list, select "Format..."
Set the file system to NTFS, which is short for New Technology File System. This is the new formatting standard in Windows, and can handle drive sizes of up to six terabytes (6,000 gigabytes).
Set the Allocation unit size to the maximum possible, which for big drives should be 4096 bytes.
Choose "Start" and continue past the warning that your hard drive will be erased.
Wait for a while, depending on the size of the drive. When it is done, the hard drive/partition will be devoid of files.

To permanently delete files you must use a program that overwrites the "empty" space on the hard drive destroying the original content. The open source program Eraser available at sourceforge will do the trick.
If you have copies of your computer's operating system on disc, you can simply reinstall the system. Doing so will automatically wipe the hard drive.
Note the files are not actually gone until another file is written to the same location on the disk. Until that happens the files can easily be recovered using tools like GetDataBack & PC Inspector File Recovery.
Many newer computers encourage that the user makes backup copies of all software on it when it is purchased. Using that copy will delete all files and restore the computer to its "new" state.
There is no need to reformat the drive before you run Eraser or a similar program.

Be sure you have a boot disc before attempting to format a drive containing vital system software.
DO NOT use this method unless you know that the drive you are formatting is not used by your computer's operating system. Windows XP has a tool for freeing up space on hard drives called the "Disk Cleanup Tool". Use that instead.

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