I have tried to use my old, working second screen with my MBA. The setup I have is this (and please try not to laugh...) MBA: thunderbolt-HDMI adapter. Then HDMI-VGA adapter. Then VGA-VGA into monitor. Yes, I know it's a bit hodge podge but I though I would make use of what I had. So, the only new thing in here is the middle bit, the HDMI-VGA adapter. Now, the MBA knows the monitor is there, it recognises the model no, etc and I can even move the cursor over to the other screen, but there is no signal on the second screen. I have tried changing the screen settings but no difference and have it set to the recommended setting for the ext monitor (as recommended by the MBA). There must be a logic issue there somewhere but I can't make it work.