Get "Reboot and Select Proper boot device" when PC at rest

[Larry]

Whenever I leave my PC for a while I come back to a blank screen with the message "Reboot & select proper boot device or insert boot media in selected boot device and press a key". I can only turn the power off, and when I turn it back on it boots up and works fine, at least until I leave it for a while again.
Thanks for any help,
Larry

Gateway FX6860
Intel i7-2600 @3.4 GHz
8GB ram
Windows 10 Home version 1607 64 bit
OS build 14393.2068

 

[Sysnative Windows Update]

Hi and welcome! What are your Boot Device settings in the BIOS/UEFI like?

 

[Larry]

The boot priority order is 1-Hard Disk, 2-CD/DVD drive, 3-EFI Device, 4-Removable Device, 5-LAN

The hard disk drive priority and the optical disk drive priority have my hard drive and optical drives listed, respectively, after pressing enter at the prompt. The other three have nothing.

Quiet boot - enabled
Halt On - All, but keyboard

Thanks for the help.

 

[Sysnative Windows Update]

At which HDD is the BCD located?

 

[Larry]

How do I determine that?

 

[Sysnative Windows Update]

Take a screenshot of your Disk Management please.