I have an original Mac Air and today is just locked up and shut down. On trying to start up again is starts as normal, with apple start up sound and apple icon comes up - then the spinning thinker comes up and it does not progress from that point, then shuts down. I have tryed PRAM reset - no response. If I hold down Option it brings up the start up disk and I can select it - but same result.
Anything further I can try - or is it time for a new one? I have backed up in recent weeks - but is remainder potentially lost?
If your MacBook Air doesn’t turn on or start up
Try the following suggestions in order until your computer turns on:
 Make sure the power adapter is plugged into the computer and into a functioning power outlet. Be sure to use the 45W MagSafe Power Adapter that came with your MacBook Air. If the power adapter stops charging and you don’t see the indicator light on the power adapter turn on when you plug in the power cord, try unplugging and replugging the power cord to reseat it.
 Check whether the battery needs to be recharged. If the light on the power adapter glows amber, the battery is charging. See “Running Your MacBook Air on Battery Power” on page 34.
 If the problem persists, return the computer to its factory settings by pressing the left Shift key, left Option (alt) key, left Control key, and the power (®) button simultaneously for five seconds.
 Press and release the power (®) button and immediately hold down the Command (x), Option, P, and R keys simultaneously until you hear the startup sound a second time. This resets the parameter RAM (PRAM).
If the problem persists, run hardware test:
To use Apple Hardware Test on your MacBook Air:
Disconnect all external devices from your computer except the power adapter. Restart your MacBook Air while holding down the D key.
When the Apple Hardware Test chooser screen appears, select the language for your location.
Press the Return key or click the right arrow button.
When the Apple Hardware Test main screen appears (after about 45 seconds), follow the onscreen instructions.
If Apple Hardware Test detects a problem, it displays an error code. Make a note of the error code before pursuing support options. If Apple Hardware Test doesn’t detect a hardware failure, the problem may be software related.
If there is an error in your hardware test, I think it's time to contact apple.
Cheers.
P.S the user manual is under your HOME folder, user guide and information, MBA users guide.
I am having this same exact problem. I have a 2012 macbook air. It started doing this almost every time i cold boot the computer after the last osx update (or maybe it was a firmware update, forget what the last thing was the other day.) The only difference is, If i force it to shut down it ends the starup loop then it starts up like normal when i start it again. Very strange but has happened every morning since that update. Come on apple, fix your **** please, this coupled with the wifi issues plaguing this little machine make it a piece of junk...
I'm going to be selling this hunk of crap on craigslist soon if apple doesnt step up their game. worst laptop i've ever owned and that's saying a lot cause i've had some pos laptops
I found this thread, tried it, having tried all the other techno stuff first, and it worked. Woke up this morning to find all my docs, including the ones I was working on, back. Thanks so much for the advice. I am a total Luddite but love the democracy of Apple. It, and these discussions give me the confidence to give everything a go :)))
