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#11
Those mounting points are designed to be electrically connected to the chassis, hence the ring of solder to ensure a good contact with the mounting screws.
This does seem to be a strange problem, and it would seem to point to a grounding issue. Ensure that your motherboard is correctly mounted, following my advice about mounting points and screws. Check for electrical conductivity between the chassis and the earth terminal on the PSU socket. Plug the mains lead in (do not connect to the supply) and check that you have conductivity between the chassis and the earth connection in the plug. If not, check the mains lead for conductivity on the earth lead. Repair/replace if a fault is found. If you find no fault, then it might be a fault on your house wiring GET THIS CHECKED BY A PROFESSIONAL. If you have radiators in your room, then connect a wire between the chassis of your computer to the pipework of the radiators in order to provide a ground connection. Ensure that this connection is made to bare metal.