lost disk space for system backup

Hello community..

New laptop Toshiba Satellite L500. 320Gb hard disk with 2 partitions, C + D (160Gb + 160Gb)

I used the windows7 home premium backup utility to make an image of my "C" drive. I saved the files on the separate partition "D".

The program advised me that although it was on a separate drive, it was actually on the same physical drive as my operating system and as such, in the event of hard disk failure, I would be boned. All logical stuff, and I accepted and went ahead knowing that I was about to buy a new external HD. So when I got my new USB external HD, I copied the backup files from D, pasted to X and then deleted the backup from D. (After a freak powercut once at a crucial time, I never move files, I always copy then delete the original).

Question: Why have I lost the 15Gb of space that was taken by the backup image of the C drive? I have system restore turned off on the D drive. I have run M$ disk cleanup utility, also CCleaner but I am mising 15Gb. I have also done: folder options --> view --> show hidden files and folders + Show protected sytem files, but cannot see anything on the drive. Any suggestions, please?

Thanks
D

EDIT: Also, when I right click on the backup image it says it has no size at all, so I only know how big it is from knowing the hard disk free space before and after. Why is this too?

Download windirstat and see for yourself
Ill get the link
http://download.cnet.com/WinDirStat/...-10614593.html

After you get to the segments on the HD, either click or put cursor (forget which) to get more information
Dont forget the worst case scenario.
Run anti virus scan
Download and scan with Malwarbytes, update before you scan

Thanks let us know either way.
If good news you will be helping others
If bad, we can give further help
Have a nice day.

It is probably shadow copies. You can do this to delete them all but the last one (system restore points)
Disk Cleanup - Open and Use

If it did not work before, will probably not work now. You should not turn off System Restore on a permanent basis.

Try this
Control Panel>Administrative Tools>Computer Management>Storage>Disk Management

Here is how you determine the size of your shadowstorage: Open an elevated Command Prompt (run as admin) and type vssadmin list shadowstorage, then hit Enter. It will show you the shadowstorage of each Partition. The Allocated number is the amount that is currently used.