Is there a way to truly delete all deleted files?

Solution 1:

Eraser

You want to choose the wipe free space option.

Solution 2:

No need for additional software.

Drop into a command prompt and use the built-in CIPHER command.

cipher /w:C:\

1. Quit all programs.
2. Click Start, click Run, type cmd, and then press ENTER.
3. Type cipher /w:driveletter:\foldername, and then press ENTER. Specify the drive and the folder that identifies the volume that contains the deleted data that you want to overwrite. Data that is not allocated to files or folders will be overwritten. This permanently removes the data. This can take a long time if you are overwriting a large space.

Solution 3:

Actually CCleaner should do it with Gutmann secure file deletion and "wipe free space drives" enabled!