I'd go through the following troubleshooting steps and see if that helps your MacBook Air recognize the monitor:
When using an external display be sure to check the following:
- If you're using an Apple notebook, confirm the AC power cable or adapter is securely connected to the computer and the cable providing power to the display is also secure. It is always good to have your notebook connected to AC power when an external display is in use.
- Confirm display adapters are fully seated in their respective connections and that they are supported models and for the computer and display. Refer to these articles to assist you with adapter compatibility and further configuration information:
- Remove all display cable extenders, KVM switches, or other like devices and retest to determine if the issue is resolved.
- If more than one video adapter is in use—or "daisy-chained"—troubleshoot by using only one adapter.
- Example: A mini DisplayPort to DVI adapter connected to a DVI to HDMI adapter is an unsupported configuration because there is a series of adapters in use.
- If available, try using a different display and or adapter (or use a different connector by using DVI instead of VGA, for instance).
Reset the system
You can reset the Mac's parameter RAM and SMC.Reset the resolutionStart by resetting the Mac's parameter RAM. If the display does not come up, was previously set to an unsupported resolution, and still results in no video:
- Start up in Safe Mode.
- From the Apple () menu, choose System Preferences.
- Choose Displays from the View menu to open the preferences pane.
- Select any resolution and refresh rate that your display supports.
- Restart your computer.
All the best,
With a local Apple certified shop on the phone, we determined that the problem is apparently in the logic board, the video part. (Sorry the correct nomenclature escapes me at this late Eastern time.) I tried with two very different monitors and cables. Still no joy.
However, I didn’t try resetting the parameter RAM and SMC because the help file says that’s for a resolution issue, which it is not; I just want to see that elusive Thunderbolt tab. If you think resetting might help, I can give it a try. If it is not and exercise for a newbie (which I am to Mac) please let me know, and perhaps a few tips on this procedure beyond what is in the info you've kindly provied. It says to select the resolution and refresh rate, but I don’t know how that makes sense if I can't even get the Air to see the monitor. The monitor knows it has been plugged into the port, and says "no signal" when I remove it.
I’m still in shock that after purchasing my first Mac, a year later, I discover a problem with the logic board. And the repair cost makes me wonder if it is worth it to have the “luxury” of a remote monitor, unless of course something else is wrong that I am unaware of, that a new logic board would also solve.