I erased my hard drive on my 2017 IMac and now the hard drive seems to be gone! What did i do and what should I do to get my HD back?

The solution is to boot macOS Recovery again and use Disk Utility to completely erase the device.

Follow these instructions: Erase and reformat a storage device in Disk Utility on Mac - Apple Support.

Pay attention to Steps 3 and 4: Be sure to choose View > Show All Devices. The "Device" in its context refers to the entire storage device, meaning not a volume or partition subordinate to that device.

If you erased the whole physical drive as @John Galt mentioned and began installing macOS, then after the first copy phase completed, the iMac rebooted to finish phase 2 and this is where you are at now? If so, then most likely the hard drive is failing, or you may be encountering a GPU failure (somewhat common on the 27" 2017 model).

Try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics don't detect most drive failures, nor will it likely detect a failing GPU, but it is worth a try.

It may be possible to check the health of the iMac's internal hard drive by creating & booting a Knoppix Linux USB stick. If the diagnostics don't report any issues and you would like instructions for checking the hard drive using Linux, then let me know. You will need access to another computer (Mac/Windows/Linux) in order to create this Linux USB boot stick.

If you have a spare USB3 SSD, then you could instead install macOS to the external USB3 SSD instead. We could still check the health of the internal hard drive to confirm my suspicions as there are some utilities available for macOS to do so. If the internal drive is failing, then the easiest solution is to boot & use macOS from an external USB3 SSD since it is tricky replacing the internal drive.

My money is on a failing hard drive, but either item is a possibility.

If you selected the View menu > Show All Devices, and literally nothing appears in Disk Utility's Sidebar, then the Mac's built-in storage has failed. Please confirm you are actually seeing nothing in the Sidebar.

Why did you erase the iMac?

If you want to start over, sell or give it Ito someone,

see > What to do before you sell, give away, or trade in your Mac - Apple Support

Hey there, to get your iMac back and running again make sure to go into Disk Utility and format your Hard Drive to Extended Journaled assuming you have wiped your Hard Drive. Exit the page and reinstall the OS as normal.

Hi there!

Did you use Disk Utility to erase the disk? Could you upload a photo of what you see?

Jack

It may have died, get an external drive to install to.

I'm unable to assist you any further, I'm currently having similar problems with one of my iMacs I own.