Hi, I have a new Acer monitor, model is S240HL. I am connecting my Mac to it via an HDMI cable and an HDMI adapter. I have used my Macbook Air, the HDMI adapter and the cable many times in the past on my TV -however when I plug into my Acer monitor, the screen on the Macbook Air flickers but nothing happens. Display settings don't show a second monitor, and nothing comes up on my monitor. The monitor works fine with my other HDMI connections! What to do?!