Run disk cleanup ( cleanmgr ) and see what it reports for space that can be reclaimed.

Try using space sniffer.

It’s probably windows system restore point or something like that.

Treesize is another good one, scan and delete.

Perhaps it was accumulated temp files and windows updates. Are you using OneDrive? Perhaps it’s cleared out a bunch of files you’ve not used in ages?

Is your PC prepping to install Windows 11?

Several possible reasons, so I’ll order by likelihood, and multiple answers may be compounded together as correct:

1. You’re mistaken on how much space you had, I dont see a reason for you to look at the exact number before shut down and then again on log in, unless you were expecting something.
2. You really need to clean temp files
3. Windows, driver, software, game updates/ leftover files
4. Onedrive or another cloud sync software auto downloading stuff
5. Something you’ve downloaded recently that actually used a lot more space than you anticipated (download size do not correlate to disk usage, compression is ubiquitous over downloads)
6. Possible malware.
7. Hardware failure (corrupt file table or corrupt files creating bad reads, or sectors too damaged to use)

pretty sure its the pagefile

Do you use editing programs like Photoshop? If its running in the background it’s likely creating temporary files in your drive. You can change the directory it uses in settings, too, if you want to have more space. Even if you’re not using that kind of apps, you can still go to the windows search bar and type “%temp%”. You can delete everything from that folder without much worry as your computer has a backup of these files and can generate them again anytime. I’m not much of a tech guy myself but I know that much. Correct me if I’m wrong tho!!

We can’t answer you because we don’t know what you use the C: drive for.

30GB is the size of a game from Steam, for example. You may have been browsing online and cached lots of large files. It could be cached updates. It could be new programs.

What you can do to check for temp data is to run Disk Cleanup and use the system option. See how much space you can recover, but if your machine is pending a reboot from patching (patch Tuesday was last week) complete all your updates first.

When windows does a major update it creates a rollback folder for the previous windows install.

You don’t say which windows version you are running but 23H1 just released for Windows 11 so that would line up.

If you run disk clean up and select the system files option you should see a previous Windows version listed.

Check your PC is running properly before clearing it though as you won’t be able to roll back once you have cleared it.

Check your windows system restore settings. If it hasn’t been messed with before, it will keep taking up space until you either change it, or there’s nothing left.

There’s just too many blanks here for people to be able to help you.

What kind of programs do you use? Video editing? I’m sure not.

Anyway, do what other people said. There are many “show me where the disk space is” kind of programs. I use Tree Size Free, it shows an explorer-similar view with a graphical interface, and sorts the folders by size in disk.

But even with this type of programs, you may not know how you went from 90 GB free, to 62 GB.

You need to tell us more of how you are using your computer, what did you do the day before, and what did you do after.

One thing it could be, is one of your programs using more ram than you have. In that case your C-drive may have been used to store what didn’t fit into the ram. Some times you’ll get the space back once the data is no longer needed or when you close the program, but in my experience, I often have to restart the pc for all of the space to be free again. That also means, if you have already tried restarting, than I think we can rule this possibility out.

First place I would look is the windows temp folder.

As others are saying. Use wiztree and scan the c drive. Figure out what folder is taking up space and go from there