I have accidentally put an AvenirNext.ttc (font file) to Windows Fonts folder (C:\Windows\Fonts). At first, no change was visible. Only the next morning when I turned the computer on, the system font was complete gibberish. Sample image provided below. So I thought I would check the font folder. And it was wiped clean with the exception of about 3 font-files. I couldn't read the font file names since everything's gibberish.
So I copied all fonts from another computer and put them to the Fonts folder of my "broken" computer. It instantly resolved my issue. All text is readable again.
But the issue hasn't really gone away. Every time I restart my computer, the font is back to gibberish. I can't remove the .ttc font file since I can't see it in the Fonts folder.
I tried to find a solution online...
I tried to restore default fonts... restarted computer and nothing. I deleted all fonts files and put only a few system once in the Fonts folder... restarted computer and nothing. I deleted FNTCACHE.DAT (font cache file)... restarted and nothing.
The giberrish is still there on restart.
I am running out of ideas how to fix this.
Any tips would be greatly appreciated.