You could have a ad video card. I would check that, also the VGA cable that goes from the computer to the I/O board from the I/O board it goes through relays and is then RGBHV. Have you check the RGBHV cables?
I had the same problem in a night club in Montreal, I suggest you to check every cable inside the dl.2, and if it's not a cable issue then it's maybe a bad video card.
