unknown file using a lot of space

I'm at a loss as to what the file could be...

On your second screenshot, you have the file highlighted in the left column but it doesn't highlight any file type in the right column.

Do you by chance have any benchmarking programs or do any of your video / audio apps write temp files to your disk during transcoding or editing? Try looking at the date when the file was created and see if that date corresponds to any transcoding / editing you were doing on that date. I understand that you don't want to just delete files willy-nilly, but it may turn out to be just an innocent temp file.

Well, without knowing what you use, you might begin with those programs and look into the preferences or options to see how the program handles transcoding or writing files and see where those files are written to. Also, see if the program clears the temp cache after transcoding or writing files.

I am only guessing
It is possible that it is not a single file, but several files and or folders of unknown type.

Could be System Restore files?

Since they do take up drive space, but the files are inside a locked hidden folder "System Volume Information" but still be read as taking space.

and/Or Shadow Copy?

Shadow Copies (restore points) are not shown in WinDirStat. If you want to see the shadowstorage, open an elevated command prompt and type (or paste) vssadmin list shadowstorage, then hit Enter. Look for C and Allocated. That is what the restore points (shadows) currently occupy.

But there could be also other shadowcopies on other disks/partitions (if you have enabled it - which is always a good idea for data recovery).

lartomar2002 said:

so i should delete all restore points except last one?

No reason to delete them unless you need the space. The more restore points you have, the better.