I've set the option to Never turn off the Hard Disk (Power Options; Advanced settings; Hard Disk; Turn of Never). Also “Hibernate after” is “Never”.
With these settings, there is some sort of pattern emerging in regard to the length of time in “Sleep” and if the PC will wake up or not.
For experimental purposes, I’ve set “Sleep After” to one minute. Once the PC has gone to sleep, I’ve noted that for sleep times less than two hours, the PC will wake correctly. If I wait above 2 hours before waking the PC then it is likely to fail to successfully come out of sleep. If I wait for 3 hours or above, it always fails to come out of sleep. When it fails to come out of sleep then initially the log on screen is shown but during the time I type a password, then an error message is displayed. If no applications were open before sleep, then the error message is symerr.exe, otherwise the error message is about Chrome or Norton (nis.exe).
Following the Windows error message, the PC then shows a text screen : Windows boot manager; Windows failed to start; status 0xc000000e; The boot selection failed because a required device is inaccessible.
I then switch off the PC using the front panel button and then remove the mains supply. I then switch the mains back on and then press the front panel button, the PC then starts correctly with the log-on screen.
I am coming to the conclusion that Crucial-CT128M part number CT128M550SSD4 and the Gigabyte motherboard GA-H97-D3H are for some reason incompatible and I should not use the M.2 socket for the OS.