I'm hoping that I have fnally got to the bottom of this, I think it's the combination of which port I have the monitor plugged into, and the BIOS settings for graphics adapters. I had assumed that the words "Init display first" on the BIOS setting meant it would try one then the next and so on. Instead I think it means that if you have multiple displays, whichever you select here will be treated as primary monitor, anything else plugged-in will be secondary. What appears to happen is that if you select something here that relates to a graphics port with no monitor attached, it looks no further.
Extra confusion has been added by:
- "load optimised settings" sets the BIOS to a combination of settings such that I will get a blank display if my monitor is plugged into any of the onboard graphics ports (so would "load fail-safe") because "PCI" is the default
- having said the above, when I first booted the system after assembly, I got a display, it was only on subsequent boots that I had problems, I have no explanation for this
- one day booting gave me an error beep code every time, seems to have been fixed by flashing the BIOS to F7, so I'm going to ignore that it ever happened
I've done some experiments with settings this morning, booting into Memtest on CDROM, hoping this wee table will make sense:
BIOS option setting combinations tested
combo1 combo2 combo3
Internal Graphics Mode UMA Disabled UMA
Onboard VGA Output Auto - Auto
Init Display First PCI PEG OnChip
Results were:
Monitor connect to GPU DVI OK OK Blank
Monitor connect to OnBoard DVI Blank - OK
I currently have it set to "combo2" above and will reboot periodically through the day and see if there are any failures.
Must remember if loading optimised settings, to rejig the graphics setttings !