A good friend of mine, let's call hir "user", asked for advice since hir PC refused to apply updates and complained about low disk space on "C:". I sent the following instructions:
Press Win-R to open the "Run" dialog, type cleanmgr [Enter] or click [OK]. When it offers to compress old files, don't. All else is fine. But you may want to make sure you have "Windows update cleanup" checked (see screenshot). Screenshot: http://fam.tuwien.ac.at/~schamane/.../resources/disk_cleanup.png
Then I received the following reply:
I wanted to use the link you sent but when I click [OK] in Disk Cleanup nothing happens.
We all know these stories. But it's still bamboozling every time it happens for real, and one of your own users is the main actor ;-)