My 2010 MBA cannot connect to any external monitor via the mini displayport. I am running Mountain Lion and Windows 7 using rEFIT. I've tried 3 seperate adapters, DVI, VGA, and a dual DVI/HDMI adapter. None of them are official Apple ones for what it's worth. I don't frequently use this but the last time I tried was over 2 years ago and it worked great. The only difference at the time being I was running Snow Leopard. Neither of the systems detect any external monitor. I am absolutely sure my tv/monitor is tuned to the correct input as well. It is simply as if there's nothing attached. I cannot change anything in the options to configure an external monitor because it's as if its not there. This happens in both OSX and Windows. My last ditch effort is to try reinstalling everything from scratch and forgo rEGIT (is it possible that's the problem?). The nearest Apple store is 3 hours away and out of warranty so I want to discount all other possibilities before going there. I've tried an SMC and PRAM reset.