video suddenly posterised/dupe monitors in Dev Manager?

[Asp]

Sometmes my video suddlenly becomes posterised:

instead of smooth colour graduation, I see banding.

I haven't made any changes in video settings.

This has happened before, and then later, as mysteriously, it somehow reset.

I have onboard Intel graphics video, which I thought was pretty foolproof, and a LED monitor connected by VGA.

Don't seem to be any user settings I can play with, except the colour depth screen settings, which I changed from 32 bits to 16 then back to 32, in case that was the problem, but it looks the same. Also rebooted of course, but that failed to change anything.

I have the feeling this change came after watching a Youtube vide, so it may be something Flash related.

I realise this is hard to diagnose at a distance, but maybe someone has a clue of what is going on.

-- I just noticed in Device Manager that I have two monitors listed. Appear to be duplicates, "Plug and Play Monitor".

Is that normal?

According to the "Intel Graphics and Media Control Panel" I have only the option for "Single display" anyway.

I uninstalled them and let the system search for new devices, and it came back with the two monitors again.

-- Another PS: I shut the PC down for an hour and when I restarted the video was normal.

Could this be hardware?

I still have two monitors in Device Manager, so whatever that means it's not the cause.

Next time it happens I'll try rebooting with a LInux CD.

Edited October 31, 2013 by Asp

[Tripredacus]

I wouldn't worry about the monitors in Device Manager. If you wanted to clear yourself of anomalies there, reboot into Safe Mode and delete all the items under where the monitors show up. The reason for Safe Mode is that there may be more devices that appear there.

Which motherboard do you have and what display do you have?

[Asp]

Sorry for the delayed response.

I haven't noticed the "posterising" since my initial report.

However, not long after I had an issue with my power supply.

The house's circuit breakers tripped and when I reset them and restarted the PC, the fan was extemely loud.

Don't know which is cause and which effect, but it seemd a bad omen so I replaced it. So far working fine, and no further video glitches.

I've learnt that power issues can cause any number of weird effects.

New PC, about 4 months old.

The mobo is Intel DH61WW.

Monitor is Acer AL1715, VGA connector, 1280x1024 pixels.