High Sierra install issues and now can't find startup disk

First, reset the NV/PRAM by holding Cmd + Option + P + R when powering it on. Allow the unit to chime twice then you can release the keys. Then immediately try booting into recovery mode by holding Cmd + R when you power the machine on.

Once you get to the recovery menu, try to reinstall the operating system. Resetting the NV/PRAM will clear out any temporary installers that are stuck in temporary memory, and hopefully you will be able to do a clean install.

Best of luck!

My MacBook Air also had the ? screen while updating to High Sierra with 30 mins to go. I followed the instructions on If a flashing question mark appears when you start your Mac - Apple Support and started up the computer using CMD-R. I did not see my startup disk in the Startup Disk window, so I opened Disk Utility from the macOS Utilities window, and clicked the First Aid tab. But there was nothing to repair - the disk was fine. I quit Disk Utility. Still no Startup Disk. The next suggestion was to try reinstalling macOS on your startup disk. What I was afraid of was that this would erase the data on my computer, for which I had no back up. Thankfully by chatting with Apple Support, I learnt that the option "Reinstall macOS" in Mac OS Utilities does not erase the data on your computer, so that's what I did. The reinstall of High Sierra was successful and my computer is up and running again!

Solved:

Recovery, internet recovery, complete formatting, reset PRAM, diagnostic boot all not working?

Make a bootable usb stick if you haven’t already. Boot in it. Open disk utility. Press PARTITION. It’ll give you a prompt to make a container inside the apple file system. Choose the other option. Now select Mac OS journaled (NOT APFS) and wipe. Reinstall and boom! You’re cooking with fire again.

Looks like older macs are somehow getting formatted to the new file system, then the machine can’t identify where to boot. Hope this helps anyone!

from Apple customer support:

"Andrew

No worries, I'm going to do everything I can so we can resolve this together! To start out, on your MacBook Pro, let’s power it off, then power on while holding Command-Option-R until we see a globe appear.

Andrew

With this step, your Mac is booting from a networked partition, and we can reinstall macOS from here to get things right back to normal!"

It will solve the installation error issue and will install macOS High Sierra.

Goodluck

Idf your computer has a built-in SSD, High Sierra converts the file system over to the new APFS format. Although it generally goes without a hitch, if something goes wrong it can cause some real ugliness.

In my experience, the easiest way to fix this is to boot it into Target Disk Mode by restarting while holding down to the T key, and then connecting it to another Mac and using that machine to reformat the drive and reinstall the OS. This should only be done if you've exhausted all other options and still can't get it to work from Recovery Mode.

https://support.apple.com/en-us/HT201462

Press CMD+OPT+R as soon as the system is booting up it will boot to internet recovery then hit the apple logo corner top left side of the screen select start up disk then select the disk that your are trying to boot in to then run the update on the App Store. If that step won't work go to CMD+OPT+R internet recovery on the menu bar click utilities>terminal after that type-in "date" and hit enter if the date is not setup correctly type-in "date MMDDHHMMYY" then press enter that will make your time setup correct for example date 0312130018 then go ahead and install the high Sierra without erasing your HDD so that all your stuff will be saved.

I ended up rebooting in Recovery mode following the directions here: About macOS Recovery - Apple Support, and it ended up working. Good luck to everyone!

Holding the D key should bring up Apple Hardware Test. It sounds like a problem with your hard drive.

If a flashing question mark appears when you start your Mac - Apple Support

Try booting into Recovery and run Disk Utility > First Aid. Let us know what it reports.

About macOS Recovery - Apple Support

Brought to Genius Bar, they determined my hard drive bracket/connection is faulty. I know coincidences exist in life, but find it odd it failed within a day of the upgrade. It’s possible though, as I was able to remove my hard drive, hook it up via usb and was able to boot from it, so it could be the bracket after all. Ordered bracket online and will swap out once received and will update.

If you follow the instructions given above about booting into recovery partition, it’ll install a fresh copy of the operating system on top of the old one. It will not erase any of your data, but you should have a backup in case things go wrong (you should have a backup anyway!).

If that doesn’t fix the problem, let us know here and we can dig deeper.

I reinstalled MacOS in recovery mode and it fixed the problem for me.

I got this same problem. It can be solved by booting your mac with pressing optio-key. Now you can choose High Sierra as starup disk again. This problem is probaply because High Sierra uses different formatting type (APFS) for disk than earlier system versions (HFS+). It is possible that this problem is only with SSD-disks.

Big question is Do You Have a Backup?

I had a very similar problem installing High Sierra on a mid-2012 Macbook Pro. Unfortunately Apple doesn't tell you that this upgrade is pretty major as you are changing file systems. There are many people experiencing this or very similar problems.

I did a ton of research, none of it very helpful. Running first aid over and over did nothing, and you can't reinstall Sierra because of the file system change made by the High Sierra install.

My solution was to get the machine back to a pristine state with Sierra installed as though you just got it and then do the upgrade to High Sierra via the App store.

Here's what I ended up doing, YMMV:

Make a bootable Sierra (NOT High Sierra) thumbdrive (How to create a bootable installer for macOS - Apple Support)

You will need access to another Mac to do this.

Boot the target machine and run disk utilities.

Reformat the hard drive (this is why you need a back-up - any data will be lost) use the default settings. In my case I had to reformat the drive and run first aid on the physical drive and volumes several times before it all looked right in Disk Utilities. In my case I could not get the mechanical drive to format properly and replaced it with an SSD (probably can't do that with an Air).

Install Sierra.

Boot the machine and go to the App store and you should now be able to upgrade to High Sierra.

If you have Time Machine, migrate the data onto your machine (I am told this works flawlessly despite the fact the Time Machine file was created under Sierra. I did not do this myself, my situation was far worse! I had to recover using a corrupt Crashplan backup. Nightmare). If you have only a regular backup, you will want to restore the data files, and then, pick and choose what you can salvage from the user library / applications / documents directories. You may lose calendar, contacts, etc., I did. Restoring some of those files can cause apps to crash because of indexing issues, etc.

Hope this is of some help. Good luck.

As I said I am not techie. I followed the Apple Care techs instructions. If you look at my picture, it says restart. I did this and it took me right back to that screen. He had me boot to recovery but that didn't work.The tech asked me to look for my disc and I'm not sure if he said startup disk or boot disc. That's when I clicked on the Apple logo in the upper left corner that does not show in the picture. That took me to a dropdown where I chose my disc and the Mac rebooted as normal. I ran First Aid and it said it was fine. I updated from Sierra to High Sierra. Please note, my Apple Care was expired but the tech spent at least an hour on the phone with me and I was called later in the afternoon to see if I was able to update.

This is what I did:

Follow these steps after starting up from macOS Recovery:

1. Choose Reinstall macOS (or Reinstall OS X) from the utilities window.
2. Click Continue, then follow the onscreen instructions....

Good luck!