Need invisible hidden file help - HD maxing out

[rdoty]

My hard drive is 500 GB and a week ago it was about half full. Then a couple of days ago I noticed the indicator had turned red - it now showed about 45 GB free space left. I immediately began searching for what could be chewing up my capacity and in the process I calculated the total Folder/file data to be approximately 253 GB, including hidden files. I've done Disk Cleanup and Defragment at least twice and gone through the file size total calculation at least four times. Still the HD was showing about 450 GB used so there was a difference of about 190 GB.
I downloaded WinDirStat and ran it and it confirmed there are 187 GB of "unknown" files....but where?
Out of frustration today I decided to do a system restore to a week ago and before I did I copied all my important files to a portable HD. After about an hour and a half the system came back up with a message that it wasn't able to complete the restore so everything was as it had been. NOT SO! When I checked the HD capacity I suddenly discovered that I now only have about 12 GB free space!!!
I need help!!
My questions are:
1) Where the heck is all this mysterious "hidden" data?
2) What would cause massive jumps in data storage in such a short time?

 

[TrainableMan]

The most common hidden data would be the recycle bin. To free up some space go to the recycle bin and empty it.

If you want to see hidden things open Windows Explorer (not Internet Explorer) & go to the Folder Options, select the VIEW tab, and choose the "Show hidden files, folders, and drives".

If you want to see even more things in the Folder Options View, remove the check next to "Hide protected operating system files (Recommended)." Please understand that if you delete an operating system file you could make it so your computer does not work properly; it possibly may not even boot up any more, so that is why Microsoft recommends you don't even show them.