Several times over the last few weeks, I noticed that my computer (Dell Optiplex 9020) had rebooted while left on overnight. Then today, without warning, the light blue (not BSOD) WIn 10 Restarting screen appeared while I was doing something noninvasive, like checking email. Then the system rebooted.

The event viewer offered the following clues:

Event ID 109
The kernel power manager has initiated a shutdown transition.

Shutdown Reason: Kernel AP

Event ID 1074
The process C:\WINDOWS\system32\winlogon.exe (MARK-9020) has initiated the restart of computer MARK-9020 on behalf of user NT AUTHORITY\SYSTEM for the following reason: No title for this reason could be found
Reason Code: 0x500ff
Shutdown Type: restart

I would be very grateful to hear back from members who have solved this problem.