I had a similar issue some years ago. Was related to the GPU card not be seated well or possible slot, card edge problem. When my wife dusted off the computer, she also dusted off the rear cables and found out just slight movement of the video cable caused the problem as it was moving the internal card. Cleaning the card edge, and reseating the card corrected the problem. Also was carefull not to move cables in rear of computer anymore and did my own dusting....lol.