DOS is the is still the base.

I have written before that many of today’s youth do not know what DOS is, but it is still needed. Now it work in the background, but before it was something that you was needed to install before you evon could start to think about Windows

Format the hard disk properly

When you format a hard disk, you make it very difficult to restore the data from the disk.
To do this:
Start the command prompt as administrator. (Go to Start, type cmd in the search box and then right-click cmd.exe and select Run as administrator)
Type “format X: / P: 5.” X, replace the drive you want to format. The number five is the number of times you want the data to be overwritten.