Problem with two PCs. What was it?

Question

Electronics

In short, two computers included in a common network filter did not show anything. Themselves buzz Windows loads the image no. When changing the angle of the monitor, the image sometimes appeared. An attempt to pull out and insert the cable brought me a spark in the face (from the VGA port) and turning off the surge protector. After twisting the VGA cable and turning on the filter, everything worked. Attention question. What was it? Or rather, what it was so that it could be stated on paper (in reporting).
Monica 1024 on 720 computers selorons vidyuha built-in two GB of RAM