So I have a macbook pro and a philips 20" hdtv. I have this dvi-i cable I was using so I can have an external display. At first it worked no seat. But now whenever I plug it in the screen on the laptop flashes to the blue screen real quick as it should and the tv itself flashes to a blue screen for a second but then the tv says no video display. How can this be? I had it working last week. Help? 