I've used Calibre for many years. But now the ebook viewer simply won't open. There are no errors displayed. Calibre seems to work fine otherwise (except edit book). I'm using Calibre 4.23 and Windows 10.
If I try to open an epub via Windows Explorer or try to run ebook-viewer.exe directly, I can see the process appear for about one second in the task manager, then disappear, but no window ever opens. If I try to open an epub from Calibre I can see the same thing happen with the calibre-parallel.exe process.
I recently had to update my display drivers, which makes me suspect it has something to do with
this issue, but I don't understand the instructions that kovidgoyal linked to.