Can't recover, can't reinstall; now what?

You can't erase the drive you are booted into. When you boot into Recovery, it is from a partition on the drive. You must use Internet Recovery to erase the drive. Restart holding down cmd-opt-R. You should see a spinning globe instead of an apple symbol. It will boot off of Apple's servers.

You can use Disk Utility in IR to erase the drive as Mac OS Extended. Then try to reinstall (from within IR).

It's entirely possible that your drive is failing.

Wait for the startup tone before holding the keys.

The wireless keyboards don't trigger correctly if you hold them before the tone.

What model year is your iMac? IR will only work with 2011 or newer.

Hi Timothy,

When your iMac upgraded to macOS High Sierra, the existing Mac OS Extended Journaled partition (your startup disk) on your Mac was converted into an APFS container, containing the following volumes:

• Preboot (used for FileVault pre-boot authentication)
• Macintosh HD (your actual startup disk with all of your data)
• Recovery (where Recovery Mode gets stored for each volume)
• VM (storage for sleep images)

The reason why you're getting the APFS volume error is because macOS Sierra doesn't support starting up from an APFS volume. It must start up from a partition formatted as Mac OS Extended (Journaled) or its variants. In order to install macOS Sierra or an older version of OS X onto your Mac, you must reformat the entire APFS container. To install macOS Sierra onto your Mac:

1. Boot the version of Recovery Mode that shipped with your Mac over the Internet, or image a copy of macOS Sierra's Recovery Mode on a USB flash drive and boot that instead.
   1. To boot the version of Recovery Mode that shipped with your Mac over the Internet, hold down Shift-Option-Command-R as you turn on or restart your Mac. Release the keys when a spinning globe appears, or when you're prompted to connect to a Wi-Fi network.
   2. If you have another working Mac, and wish to image a copy of macOS Sierra's Recovery Mode onto a USB flash drive, the instructions for doing so can be found here. You can open the hidden App Store page for macOS Sierra by clicking here. Once you've created your bootable installer, connect it to your iMac and hold down the Option key as you turn on or restart your Mac. Release it when you're given the option to select a startup disk to boot. Use the arrow keys to select Install macOS Sierra, then hit Enter (Return). Do not disconnect your bootable installer until your iMac has shut down or successfully been repaired.
2. When the main Utilities window appears, select Disk Utility and continue. Eject your backup drive before proceeding to ensure it can't be erased by accident.
3. Click on View, then select Show All Devices. Select the top level of your internal drive, and click Erase. Format as follows:
   1. Name: Whatever you want, default is Macintosh HD
   2. Format: Mac OS Extended (Journaled)
   3. Scheme: GUID Partition Table or GUID Partition Map
   4. WARNING: By proceeding with the next step, you will irreversibly destroy all the data currently stored on your iMac, including other partitions such as Windows via Boot Camp.
4. Click Erase. When the erasure is complete, quit Disk Utility.
5. Select Install macOS or Install OS X. You'll be guided through the installation process. When your Mac arrives at Setup Assistant, it is safe to remove your bootable installer if you used one.

   If you're offered to install a version of OS X that is older (earlier) than macOS Sierra, continue anyways. Step 7 addresses this issue.

6. If you installed macOS Sierra onto your Mac, transfer your data from your Time Machine backup disk when prompted. Otherwise, don't transfer any data and proceed to step 7.
7. If you installed a version of OS X older (or earlier) than macOS Sierra, visit this reply on your iMac and click here to show the hidden macOS Sierra page in the App Store. Install macOS Sierra, then use Migration Assistant on your Mac to transfer back the data on your Time Machine backup disk.

Hope this helps!