Hi
If you really want to have your computer completely clean then the only way to do it is to format the hard drive and start all over from scratch, or better yet just replace the hard drive with a new one, and reinstall Windows.
Almost everything you do leaves some trace behind someplace, especially if you have an existing backup made before removing the material.
A recovery program will even see all the recently deleted files.
This is why everyone should make system image files at regular intervals.
If you get a virus or install software that messes up your computer you can overwrite the whole drive with the image file and it will be back just the way it was before.
Mike