Very strange blank screen behaviour at boot time and beyond.with AMD A8 CPU

I have a desktop computer running an AMD A8-5600K CPU and it is frequently showing a black blank screen at boot up. I can boot the PC from power on but I do not see any BIOS / UEFI messages. (I can't enter BIOS or UEFI screens either.) Occasionally the first thing to come up on the screen is the windows load screen, but 9 times out of time NOTHING EVER comes up on the screen!  I know the PC is starting up and loading windows because once it's up I can remote into it using Teamviewer (and then I discover it seems to be locked into a screen resolution of 640 x 480 !!).
I have tried new cables, VGA, and DVI to two different screens - none of them work. (But I know the cables and screens work with other PCs.)  I updated the Windows 10 drivers for the Radeon HD APU (which made no difference and separately I tried it with an nVidia graphics card but none of these actions made any difference.  I don't really think this is a Windows problem because even with hard disks disconnected and after removing and replacing the motherboard CMOS battery I still get no BIOS/ UEFI screens or messages. On the one time in 10 that it did work it worked perfectly at usual 1920 x 1080 resolution. I was able to restart it from there and it came back OK but after a shutdown it was back to blank screen . Exasperated !
Alan BatemanDirectorAsked:
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RobertSystem AdminCommented:
My guess is it is a bad motherboard but that is just a guess as troubleshooting something like this usually requires hands on / spare hardware.

Some questions to ask yourself  / things for you to think about or look into:
Are you getting any audible tones during power on?
If you tried multiple video cards (when you tried them did you use the same slot?)
Was anything changed on the system just prior to the start of the issue?
Do you have another PC/MB that you can try the processor in?

Some motherboard manufacturers provide software that allows you to view system health and bios settings from within windows.
You could also try applying a bios update (assuming you can find an online one that you can load from windows).

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dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
This has happened recently in the last week?  And you are running Windows 10?

This may be caused by the latest Microsoft patch for fixing Meltdown and Spectre.  See  https://betanews.com/2018/01/08/microsoft-meltdown-spectre-patch-bricks-amd-pcs/  It will lead you to the Microsoft forum where others have complaints as well.  I'm not sure if your processor is mentioned there or not.
Alan BatemanDirectorAuthor Commented:
Never really fixed this.  Bought a new computer .
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