windows 7 - Where has all my drive space gone?

I selected all folders, right-clicked and picked Properties. It shows me all files and they total up to 45.7 GB.

But then I look at My Computer and see that I should have 74.4 GB:

Where has all my space gone?

P.S. As you can see from my first screenshot that I turned on every conceivable option to show everything, but here is the Options dialog.