Windows 7 hiding drive space?

Ive got an issue with windows 7, its reporting 12.5 gb free of 68.51gb available on drive C:
That means over 50gb used for win 7, office and assassins creed seemed a little excessive. Thought I would check it out and see what folders are excessivley large and try to track it down. Ive un hidden all files and folders and drives. Ran thorough disk clean ups including restore points etc. If I add together all my folders on drive c: they leave a large chunk unnaccounted for. All expressed in GB below

0.14 ATI folder
1.74 programs folder
0.26 program data folder
8.53 program x86 folder
3.04 users folder
16.7 windows folder
0.01 few odd files in the main C: drive

Ive not listed any folders that are empty.
So thats a total of 30.42GB accounted for.
Means I should have 68.51 - 30.42 = 38.09GB free space.

Can anyone tell me where the other 26 GB has gone? Maybe something has stayed hidden, Id like to know what as 50gb is way too big for win 7 pro 64bit.

 

OK, sorted it. Forgot to uncheck hide system files tab. Was huge pagefile.sys and hiberfil.sys
Few tweeks and I have all but 2gb back, left that allocated for pagefile.sys