Something has stolen 11GB from my disc space - Sorted - it was system restore

[#1]

I just spotted the disk space warning on my C partition which said I had only 8.35GB free of 97.6GB so decided to investigate
Operating system Win 7 64 bit
These are the results - with hidden and system files set to show

windows 	42.5
programs	3.37
programs (x86)	2.43
nvidia	        1.75
garmin	         0.74
users	        9.34
page file	 0.2
hyberfil.sys	6.25
prog data	4.48
recycle      	6.8
Total	       77.86

To add the System Information Volume shows as empty and that was where I would have expected the restore files would be

[#2]

https://windirstat.info/index.html may help you find exactly what is taking the space.
If windows\winsxs is huge have a read of https://support.microsoft.com/en-us/kb/2795190 (Google will find you loads of other information)

[#3]

crikey 25GB - will have a read
Ran System Cleanup didn't seem to make much difference although it took a long time doing it
Another check - that folder size hasn't changed
Didn't realise I needed to do a reboot 
After a very very long restart  I now have nearly 28GB free and winsxs is down to 15GB and Windows only 31GB