Running chkdsk will tell you how many disk sectors are being used for different purposes, such as files and folders. Then all you've got to do is find that files and folders. They might be inaccessible or hidden.
The usual tools:
a. a program like treesize or clduw (both free downloads) to give statistics on everything you can see
b. the (i)cacls-command to give you access to the inside of folders like System Volume Information that you normally only see the name of
It takes some time, but I would be amazed if it can't be found.
My hard drive space mysterious falls, even though I don't add or remove programs or data. It has now fallen to very low level and there simply isn't enough on the computer to use even half the the space. Sometimes I delete files still find the space actually declining. Now it is suddenly down to a very low level and I've no idea why.
I have read many discussions and taken all the recommended steps with no effect. Specifically, I have:
1. stripped virtually everything optional off the computer
2. run virus and trojan checkers
3. run disk cleanup and cclean to reclaim space and remove restore points
4. set only a single restore point
5. set the shadow copy to only 500 mb
6. searched files, including hidden files, and can't find anything unusually large
The unusually event recently is that I got a message saying that my windows copy was not genuine (which it is) and had to have it verified.
I'd appreciate and help