MacBook Air won't power on, except I remove the battery and plug it back in (SMC reset?) - sleep works
I have a bizarre problem with my 2012 MacBook Air 13":
At some point, a couple of weeks ago, it suddenly stopped turning on. The battery would charge, but pressing the power-button just wouldn't have an effect. I clearing the SMC by pressing Shift-Control-Option, which didn't have any effect. I tried different power adapters.
Then in a last-ditch effort I decided to open it up. Much to my surprise it did boot up just fine after: disconnecting the battery, pressing the power button (with AC not attached), reconnecting the battery, reconnecting AC power, and pressing power.
The weird thing is that everything (including the power button, going to sleep etc) just works, just when I shut down OS X completely, the same problem occurs (all the times), making it necessary to unscrew the bottom and do aforementioned procedure again ;)
Have anyone heard of this problem before? Are there some specific components on the logic board that could be causing this? (I am not sure if it's worth having this repaired through official channels.)
Update: To clarify the symptoms when the Air doesn't boot up: black screen, no fan, no keyboard backlight (or anything else that would indicate that it is running).
There are two possible causes these symptoms:
Faulty Battery
Bad SMC Chip (Logic Board)
Faulty Battery. As the OP described, once the battery was disconnected, the machine booted fine. What could be happening here is that the battery life has degraded to the point where it will not hold a charge above the threshold to power on the device.
If you can power the MBA in this manner, try resetting the SMC then reconnect the battery. If it continues to fail, you probably need a new battery. If you already know how to open the MBA and disconnect the battery, you are halfway to replacing it. If you're not sure, ifixit.com has an excellent tutorial.
Given that the OP's machine is a 2012, it would mean the battery is pushing 5 years now which is around the EOL for this battery. It's time for a replacement. I recommend getting one with at least a 18 month warranty.
Faulty SMC. There is a possibility that the SMC (chip) is faulty. The first thing to attempt to diagnose it would be to run Apple Hardware Test (AHT). Hold the D key while booting from a powered off state with the AC adapter connected.
It may come back with "no errors" so the positive diagnostic test would be to attempt with a known "good" battery. If it continues to fail after the battery is replaced, there's a high chance than the SMC is bad. It's time to take it in for service.