HD has 68 Gigs free, yet only shows 45 gigs

[budWindows7]

Hello.
The C drive in my computer is 139 GB (150 GB hard drive).

Windows shows that there is 45.5 GB free, but if I select the contents of the drive and check the properties, it says that everything on the drive is taking up 70.8 GB on the disk.
But in doing the math (139-70.8 = 68.2) it looks like there should be 68.2 GB free.
There are no files in the recycle bin, and I can't imagine that there are 22+ GB of hidden files.
Where did that 22+ GB go?

I'm sure I'm missing something fairly obvious here, any help would be appreciated.
Thanks
Windows 7 Ultimate x64

 

[cyclic]

Have you taken hiberfil.sys, pagefile.sys, restore points ? and other hidden files. Also often the disk space required will be more than the file size for example, depending on how the drive was formatted, all small files take up a minimum of 4K or one block. Files of say 1.50 Kb will take up 4.00 Kb of space, the properties of the file will give both figures and believe me there are thousands of small files on your drive.

This program can tell you whats taking the space

Defraggler

 

[budWindows7]

Thanks for the reply.
The trick was not only viewing hidden files, but also un-checking the option to hide protected files.
Now I see them all, and the capacity makes sense now.
Thanks for your help