I have a new 2012 MacBook Air (just a week old). Today I tried to connect to an external LCD projector, using a mini-DisplayPort-to-VGA adaptor, to project my slides.
Something went wrong and I was unable to project. My Mac detected the external projector, and I was able to mirror my main display, but nothing showed up on the LCD projector, despite trying two different mini-DisplayPort-to-VGA dongles. In the end, I was able to successfully project from a different, older Mac using one of those dongles, so I don't think the dongle is broken.
What should be the troubleshooting procedure, if this happens again? Does the new 2012 Air require any sort of different procedure or equipment for mirroring your display onto an external projector?