Macbook Air sierra update installation failed and my macbook doesn’t open? Screen shows file folder with question mark and blinks

Before you do what Lexiepex says, I would reset your NV/PRAM. It will remove any OS installation that is currently in memory. If you do not do this, it may continue to happen, as the error will be held in your NV/PRAM.

To reset NV/PRAM, hold Cmd + Option + P + R when you power on the machine. Continue to hold the buttons until your machine restarts and chimes for a second time. After you hear the second chime, release the keys and hold down Cmd + R to boot into recovery mode then follow Lexiepex's instructions.

Best of luck!

Not necessarily. Resetting the NV/PRAM will not cause that. I cannot guarantee however, that the failed installation did not cause it. It shouldn't have, but again, I can never guarantee that when an installation fails. I would just try it again, as right now, as far as we know, all of the data is still there.

If it doesn't work a second time, then there is a possibility that there is an issue with the hard drive. Reason being, the OS installation has to install the operating system on the entire hard drive, so if there is a small sector of your hard drive that is failing, it would trigger the failure of the OS installation. In that case, I would try to run Disk Utility from the Recovery menu, and click Verify Disk. If it comes up with a red-colored response, I would recommend taking your machine to an Apple store or AASP (Apple Authorized Service Provider) to allow them to run diagnostics on your hard drive and troubleshoot from there.

Good luck!

CrashBurner

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Sierra or HighSierra?

Start the mac while holding the CMD+R keys, it is slow, when it starts, from the menu select Install macOS. Then the OS that is installed will be installed again.

Normally re-installing from the Recovery Partition. will leave your data alone.