Just to dissuade to all too often malware suggestion Windows 10 is basically an experiment Beta version of an OS. Most likely this is caused by bad OS driver code not malware. It is intermittent and happens asynchronously. Microsoft just released a bug fix update 9/29/2016 - Yes applied next day but I wanted to detail my experience being a techie myself:
Events leading up to the black screen:
I think this one is the main cause:
The order is descending time typical event log sorted reverse chronological:
HAL Event Id 13 The system watchdog timer was triggered.
The Group Policy Client service did not shut down properly after receiving a pre-shutdown control.
The previous system shutdown at 1:02:50 PM on 10/1/2016 was unexpected.
The last shutdown's success status was false. The last boot's success status was true.
I underlined the previous system shutdown because I never initiated that
The system was idle at the time other than potential scheduled tasks and background daemons.
My guess is a bug with the 1607 build of windows 10 code.
I hope the recent update applied today will handle this nasty problem.
Anyone without a malware based suggestion - The system is protected by Norton Internet Security latest updates a UAC is active as well.
The big question is does Firefox latest version 50.0b3 64-bit version have anything to do with this problem. I noticed setting it as default browser seemed to make the frequency of the black screen problem more frequent than say making Edge the default browser
If malware was potentially the cause - Please show me an exploit that causes watchdog timer failure
HAL level error please otherwise I am assuming this is a Windows bug hopefully fixed by yesterday's coded and today's applied update even though no mention of black screens were made in the documentation of the fix
Cumulative Update for Windows 10 Version 1607 for x64-based Systems (KB3194496).