Chosen Solution
Hi There. Glad to be here! I have had this macbook air since 2012 and it has never skipped a beat. Until just one day it chose to not boot up. I get a green light when magsafe is connected, I followed the steps to reset my smc and the light changes to orange then back to green. afaik this means it reset fine. However holding power button, pressing power button. nothing. I get no fans, no noise, no display. Not sure what to do now, I have removed the battery and it will not start with just magsafe either. So what else could be causing it? just a side note, it’s very unlikely to be water damage. Thanks in advance. Mike.
Once you get the bottom cover off disconnect the battery and see if you can run the system directly with the MagSafe adapter. Update (03/14/2018) Here’s the IFIXIT guide to take your logic board out: MacBook Air 13" Mid 2012 Logic Board Replacement
Is the heat sink screwed on tight? I’d recommend reinstalling thermal paste on the CPU and dusting off the vents and fans
