Why is my C drive suddenly full but I have nothing on it?

As far as I know, this is a very common issue for Windows 11, Windows 10 and Windows 7. If the C drive is suddenly full without reason on Windows 10, there are several possible reasons and fixes you can try:

1. Temporary files and Windows updates

Windows stores update files, temporary setup data, and logs that can unexpectedly take up tens of GBs.

2. System Restore points / Shadow copies

Old restore points may accumulate and consume a lot of disk space.

3. Hibernation file & page file

hiberfil.sys and pagefile.sys can each take up several GBs, depending on RAM size.

4. Hidden folders (WinSxS, Installer, etc.)

The C:\Windows\WinSxS and C:\Windows\Installer folders often grow large over time.

5. Malware or junk software

Some malware or poorly designed apps create endless log files or cache data.