This thread has become a dump for MacAir 3 beep solutions so here's my addition: I worked through the following non-invasive techniques (most listed above) a couple times each and after doing 5) it started booting. Maybe they worked as a combination or maybe it was 5 that did the trick. If none of these had worked I'd have tried the Thermal Paste solution above. However, if non-invasive works, who am I to complain! Hopefully this compilation helps someone!
UPDATE: This happened to me a second time two months later: I have found a firm fix for my issue now:
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1) power off, plug in power cord
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2) Hold (left side) command + (left) option + P + R
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3) while holding them, tap power and CONTINUE HOLDING the four buttons in 2
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4) Computer will make a startup sound, KEEP HOLDING, computer will turn off, KEEP HOLDING, computer will startup again, you can let go only AFTER the second startup or even third startup.
This thread has become a dump for MacAir 3 beep solutions so here's my addition: I worked through the following non-invasive techniques (most listed above) a couple times each and after doing 5) it started booting. Maybe they worked as a combination or maybe it was 5 that did the trick. If none of these had worked I'd have tried the Thermal Paste solution above. However, if non-invasive works, who am I to complain! Hopefully this compilation helps someone!
1) "Hold Command+P+R simultaneously and press power button" (Pedro above)
2) Technique 1 followed by "hold D and power for 20-30 seconds" (relveston above)
3) "Holding down D for about 20-30 seconds -- and power simultaneously -- Then press power " (textractor above)
4) Perform SMC reset and re-verify
Shut down the computer.
Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
Release all the keys and the power button at the same time.
Press the power button to turn on the computer.
Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC. (PlotinusVeritas from Apple help forums)
5) Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys. (PlotinusVeritas from Apple help forums)