iMac hard drive deleted: What happens and how to fix?

Please tell us exactly what the problem is and what actions you believe caused the issue.

As a rule, the iMac hard drive cannot be "deleted", so I'm sure it's still there somewhere.

The drive icon on the Desktop can be hidden from view, and if that's what has happened, then the fix may be as easy as this:

Click the Desktop. Then, in the Menu bar at the top click Finder > Settings... > General tab. Make sure that below "Show these items on the Desktop" the box for Hard disks is checked.

Please let us know if that doesn't resolve your issue.

can you drag it back out of the trash (if it's internal)

or reconnect it if its external

and/or restart the machine... if Disk Utility still shows it, try clicking on it and then Mount option

I'm sorry to ay that this really doesn't make any sense to me at all.

And the age of that iMac and the version of macOS that is installed will dictate how to proceed. Unfortunately, since the Mac won't boot, you can't tell us what version macOS is running.

To determine exactly which iMac that is, find the serial number on the underside of the pedestal.

The go to View Coverage - AppleCare & Warranty and input your serial number where it says "Or, enter a serial number". The site should return info about your Mac, including the model and the year of release.

Post back here what model and year your iMac is and we can give you the best help.

FYI, never post your serial number here in the community.

Meanwhile, you might try booting the Mac while pressing the Alt+Win+R keys or Shift+Alt+Win+R keys. This might coax the computer to boot into internet recovery and allow you to access the macOS utilities there. If you can get the Mac to boot in recovery, use the Disk Utility application and run First Aid on the internal drive. Otherwise you may be able to reinstall macOS.

We'll know more when you can tell us what model and year the computer is.