1. Run this program WinDirStat - Windows Directory Statistics
. That will tell you how much is on your system.
2. Open an elevated command prompt (run as admin) and type (or paste) vssadmin list shadowstorage
, then hit Enter - that will give you amount allocated
for the shadowstorage (the area where the OS stores the restore points).
3. Once you have those numbers, it should add up to the used space. Post the numbers and we'll have a look at them.