First of all, I have the 15 inch 2011 macbook pro. I used a mini displayport to hdmi adapter to connect to both my external monitor and tv. However, neither of the two devices are recognized by my macbook and "detect display" button in the settings didn't help at all. At first, I thought I got a faulty adapter, but every time I restart my computer, the external monitor would work perfectly for 5 seconds, then it goes completely dark and cannot be detected. Any ideas how to fix the problem?