Huge chunk of Hard Drive Free Space Missing

Hello all. I could really use some help.

I have a TB hard drive with 917 GB of actual space. But right now, I only have 27 GB free. Why?

Because SOMETHING happened and now 602 GB of space has gone UP in smoke. Cannot be found.

I used WinDirStat and it just shows up a HUGE yellow box that simply says "C:" and leads to nowhere.

I then used Treesize and it doesn't even pick up the missing 602 GB. It recognizes that I only have 27 GB left out of 917 GB, but it doesn't lead to anywhere.

I have also gone into System Properties and turned down the Disk Space Usage for restore points down to 1% and deleted all previous points.

I'm on a Lenovo y580. Laptop is about 4 to 5 years old. It has never given me any problems like this before. I ran a CHKDSK recently too. It said some errors were found and fixed, but it says that every time I run CHKDSK now. This issue is new, having only occurred over the last weekend.

I'll post pictures and stuff necessary if anyone has any ideas. :) I know a bit about computers so I should be able to follow directions. But from what I researched, I don't think it's any of the super common issues. Part of me thinks it's a dying hard drive from a very old laptop, but I need to exaust every last option before I decide to buy a replacement. Money is sort of an issue.

Thanks in advance to any and all who can help with this.

Yes sir. That and I think I have WinDirStat to pick up all hidden files and folders.

Besides, what in the blue oceah could be 600+ GB? I feel as if 60% of my Hard Drive just died overnight.

EDIT: I'm uploading the WinDirStat pic.

WizTree is the best program I've found for showing the WinDirStat <unknown> files.
They have a portable version available, no installation needed.
Antibody Software - WizTree finds the files and folders using the most disk space on your hard drive

Welp. I just came back from doing chkdsk /f and /r. I lost MORE space by doing that. Now I only have 522 MG of free space left. O_o I'll need to install WizTree. I already used TreeSize and that came up empty.

EDIT: Updated with WizTree results. Same as Tree Size. The 600+ GB are just missing.

Sorry about that. I updated my info. I'm also putting a screenshot here.

My security is Trend Micro Max Security. I also run CCleaner and CleanUp! on a usual basics. If there is anymore info you need, let me know. But you might need to let me know where that info would be located. Sorry about that! I've been out of the IT game for a bit.

What happens when you run windirstat as admin? Does it still show unknown? Or at least give you a location?

There is some good points being posted here,

What is “<Unknown>”? | WinDirStat propaganda blog

Some even lead back here, but it may give you an idea.

I have seen that article before but I'll give the comments below a read.

But while I do that, I did run WinDirStat and there was no change. No location of the files or anything. Still directs to "C:".