It has happened to me a few times. Latest was this morning. Happened again. I had Chrome, Calibre, Elements Organizer, Elements Editor open, with several tabs running on Chrome. Background apps included Google Drive, Weather Network, Malware Bytes Premium, Display Fusion, Windows Defender, Everything, Last Pass etc. running.
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Went off to make coffee and when a returned a few minutes later, Left-hand screen (Digital) was black, Right-hand screen (analog) was red and everything was frozen. Did a hard boot, got the white on black message saying select boot device. Rebooted to BIOS, reselected Drive C as boot device, saved and exited. PC rebooted normally.
Some combination of those open programs prompts a crash when Fusion goes to screen saver. This must have started after one or the other of the aps was updated. Lost in the mists of time, of course.