Solved Disk Mystery

Win 8.1 on Toshiba laptop. Only 1GB documents, <500MB of software No Windows Old files, etc, Only <300MB could be free by running disk clean.

Any idea where 36GB is being utilized ?

Page file, hiberfile, system restore points most likely. You are only using 6% of a 500GB disk, not excessive in any way.

5.85GB for restore points, probably 4GB for hiberfile in relation to memory not sure about page file.

My concern was that there was something on my disk not being identified. So all seems kosher ?

Sure. Run Treesize Free. It will tell you what is using your hard drive.

You need to show hidden files as well:

XP, Vista and Windows 7:
Open My Computer, Tools menu, Folder Options.
Click on the View tab.

Windows 8 and Windows 10:
Open This PC.
Click on View tab then Options at far right.
Select Change folder and search options.

All:
Check Show Hidden Files, folders and drives.
Uncheck Hide extensions for known file types and Hide protected operating system files [Recommended].
Click Apply then OK.

Run this program - it will show all files.

Great answers - Thanks to all !