HDD space mysteriously near completely filled

Hello all, I have big problem with my Asus Eee Slate, and I can't figure out how to fix it.

First off:
Asus Eee Slate EP121
Operating System: Windows 7 Home Premium
CPU: Intel Dual-Core i5 470um
Memory: DDR3, 1 x SO-DIMM, 2GB/4GB
Storage: 32GB/64GB SSD

Whats been happening: A little over a year, and from once I got this, the tablet performed immaculately. I could do so much, including Gimp and even some more modern games. But since then, the tablet has gotten incredibly slow, and with some passing of time, I was unable to run Gimp and games slowed down to the point of unplayability. Including low end, 2-d shooter games. Then even standard operations got slow and actions laggy.

I went in and cleared out most of the stuff from my harddrive, programs and apps, music and videos you name it (I don't have a lot of photos on it). Since then, I've been only running Chrome (sometimes FireFox) and Skype. My harddrive then was still somehow pretty damn full. No idea why.

Fast forward to now, and boom, I get hit with this message:



So, I check my harddrive:



How did it get full? Anti-virus scans comes up clean, too. I've read somewhere that Windows updates take up space, but seriously, this much?

If this is a Windows update problem, anyway to fix it and get my space back? I really should have a whole lot more of space, even when the tablet was running great, playing games and such, I still have plenty, plenty of free space left!

I will be very grateful to anyone that can help me.

Thank you.

Hi and welcome to SevenForums,
Might be tough to do anything until you free some space,
You can use this to clear temp files
Save to your desktop and right click it and Run as administrator
TFC - Temp File Cleaner by OldTimer Download - Geeks to Go Forum

Run this command and see whether you have a lot of shadows

vssadmin list shadowstorage

WinDirStat would give you a good overview on what's on the disk - but it does not show shadows.

https://windirstat.info/

It is obviously not the shadowstorage. What did WinDirStat yield.

Service pack backup files, maybe? Windows.old? Windows 10 files?

Not much to go by.