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Tonyefs: So you got it playing well? Known for not knowing enough [ever], an even modest report would be welcome.
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Peterr: It could be a mechanical thing, i.e. loose connection in plug, or bad wire, any "bad contact". It could be as simple as dirt in the plug, but if it's happened since the beginning, that sounds unlikely. Is your computer / power outlet properly grounded?
I don't think it's a motherboard issue, unless the plug is loose. What you tell clearly indicates a need for physical contact or, at least, nearness. Dogs and cats etc. can create a massive amount of static electricity, not needing to be in true contact with the apparatus, but still causing "trouble". Also, a matter could be your carpets, they can provide to this point of view. You need to have your computer "isolated".
Best wishes.