Recently--like last week--we got Direct TV installed in our home on a Tuesday. On that Thursday my brother went to plug an HDMI cable into the TV so that he could play the PS3. There was a big ball of orange light, a bang sound, and his fingers received burns. The TV and game system were in use for three months prior to the installation of the Direct TV equipment. What would have caused the jolt to come out of the TV from plugging in an HDMI cable? Not only did it burn my brother, but we believe it fried the TV as well.
If he received burns, it doesn't sound like static electricity. Another common source of sparks is the so called Y-filtering capacitors in ungrounded power supplies, but I've never heard of them causing burns, just a mild tingle.
It sounds more like he ended up shorting mains phase to ground or neutral. Which would most likely mean that one of your safety ground wires is actually connected to mains power, an installation mistake that is very dangerous. I suggest you get an electrician to check it out as soon as possible, and avoid touching the equipment in the meanwhile.