windows 10 - My C Drive is full without reason

My C drive (SSD, the drive on which I installed the OS) recently shows that it's almost full.

(Japanese text says: empty space is 6.98 GB out of 105 GB.)

But when I checked by computing all the folders' size (including hidden folders), the result is as below.
(Japanese text says: size: 54.9 GB; size on disk: 45.2 GB)

I tried system file cleanup and emptying the Recycle Bin,
but nothing changed.

Would you guys give me some suggestions please?

Answer

There are several things you could try:

• Get an overview about your disk space

If you want general information about what is using disk space on your computer, you can use tools like WinDirStat which can be found at https://windirstat.net/. (There is a portable version available at https://portableapps.com/apps/utilities/windirstat_portable). Select the drive(s) you want to have information about and start the analysis. The result is pretty much self-explanatory. You get an overview of directories and files sorted by size. Additionally, you get a visual representation of the used disk space.

• Use Storage Sense

You find that under Settings > System > Storage, or just type Storage after you opened your Win 10 Start Menu

Storage Sense is the successor of the good old Cleanmanager application which has been deprecated by Microsoft (source: https://techcommunity.microsoft.com/t5/Storage-at-Microsoft/Windows-10-and-Storage-Sense/ba-p/428270)

cleanmgr.exe

• Clean up the Windows Component Store

Open a Powershell session (as Admin) and analyze your component store by running

dism /online /Cleanup-image /AnalyzeComponentStore

This can take several minutes to complete. If it gives you the advise to cleanup the component store, run

dism /online /Cleanup-Image /StartComponentCleanup

You get more information by running

dism /online /Cleanup-Image /?

• Check for the existence of volume shadow copies

List information about the shadow storage

vssadmin list shadowstorage

or get information about the shadow files

vssadmin list shadows

Delete the oldest one on your C drive by running

vssadmin delete shadows /for=c: /oldest

Alternatively, you could delete them all

vssadmin delete shadows /all

• Disable and re-enable hibernation
  The Hiberfil.sys hidden system file is located in the root folder of the drive where the operating system is installed. It is approximately as big as the amount of random access memory (RAM) installed on the computer, as it stores a copy of the system memory on your hard disk when the hybrid sleep setting is turned on.

Disable hibernation

powercfg /h off

Enable hibernation

powercfg /h on

Hope that helps