I downloaded a bunch of fonts and tried to install them by copying them into C:\Windows\Fonts with my file manager (not Windows Explorer).
Some of them couldn’t overwrite existing fonts, so I rebooted (in case something was hanging onto the file) and tried to copy the rest.
While comparing the two directories, the computer bluescreened.
Rebooted, tried again: another bluescreen.
After a few more tries, a pattern emerged. The cause was different, but the culprit named was always win32k.sys. A google for that didn’t bring up anything specific (could be a graphics card overheating, or bad memory, or a bad driver, or …).
However, it was interesting that if I just rebooted and did nothing, the system seemed fine. Starting the file manager seemed to do it—at least, if I navigated into the fonts directory. Starting a brower also BSOD’d—perhaps while the browser was initialising fonts?
So I rebooted again, opened a command line with administrative rights and started deleting most of the fonts I had recently installed. (Once I got a bit too trigger-happy: instead of dir ver*.ttf I typed del ver*.ttf—and in addition to removing the Bitstream Vera fonts, it also tried to remove Verdana! Fortunately, that font was protected against such shenanigans.
Anyway, open font folder: no BSOD. So that’s good.
Started copying some fonts back—this time differently, though. I copied a handful of fonts into another directory (so I knew which ones I tried to install) and then, since I had the files in my clipboard already anyway, opened the Windows font folder as a folder (not in the file manager) and pasted them in there. Asked me whether I wanted to replace a few (odd, I thought I had removed those first—perhaps not—or maybe it went by internal font name, not filename, and there were duplicates? was that the problem, two font files claiming to be the same font?).
But then: Windows told me that three of the font files couldn’t be identified as fonts!
Yay! This check didn’t happen when just copying the files into the directory “behind Windows’s back”.
Copied a bunch more files in; the folder window stayed open. Started browser: no problems here any more, either.
And I’m glad that my computer isn’t BSODing on my any more!