What Apple says itself on this error:
A folder with a flashing question mark means that your startup disk is no longer available or doesn’t contain a working Mac operating system.Apple
Apple then shows instructions to use Disk Utility and/or Reinstall macOS (don’t forget to backup before of course).
For me this was not sufficient. On Reddit there are various causes and solutions. Like:
- Reset NVRAM / PRAM
- Booting with the option key to select the proper booting hard drive
- Your Harddisk connection cable is broken. Older MacBooks like the ones before 2012 sometimes have separate connections cables the can be replaced (by an expert or yourself if you’re confident enough – risk of breaking things of course). For newer ones the Logic Board might need to be replaced.
- Your harddisk is broken / corrupt. For some models like MBP’s of around 2015 and earlier you can let them replace / replace then yourself (if you’re handy enough).
What I did: resetting the NVRAM to get it working again (temporarily)
Reset the NVRAM / PRAM. On older MacBooks this is holding Option + Command + P + R when pressing the power key. Newer Mac Computers don’t have this.
For me it made my computer working for a while.
Then, after a while it turned off again and showed again the question mark folder on startup.
And then, workaround with option key (temporarily)
After that, I tried to check if I can select a boot drive by starting the Mac by pressing the Power button and holding the Option Key. Fortunately, the disk was still found. When selecting it, the laptop booted MacOS again. When switching it off, it booted again without the option key. It seemed like the problem was solved.
Still problems, getting a Panic Error:
After a while the laptop switched off again automatically. When turning on, I received an error like:
panic(cpu 0 caller xxx): AppleAHCIDiskQueueManager::setPowerState(yyy : zzz, aaa -> 0) timed out after bbb ms ...
What I did then:
Various solutions are given on the Apple Forum.
- Deleting some recent large files, likely that it caused nothing.
- Installed a recent Software Update
- Disabled Power Nap.
Unfortunately, all these solutions did not work for me.
How I got it working again:
I screwed open my MacBook, and checked if the SSD was still connected well. You can only do this for older MacBooks. And only do this if you are handy enough. For example check this guide for a 2015 MBP Retina 13″. I found out that a screw under the SSD was loose that perhaps could have made contact with the SSD. When tightening this screw and connecting everything again, the MacBook seemed to work again without warning.
Fortunately, this worked for me, but it is likely that the reason for showing the question mark in other cases is different.
It could also be the hard drive cable (for even older MacBook that have a loose hard drive cable). See Reddit.
Use these instruction at your own responsibility of course. You might damage your hardware or yourself.