HDD corrupted after using BootCamp

Repair macOS Hard Drive with Disk Utility

Steps to repair a failing Mac hard drive are discussed below:

Step 1: Reboot macOS and immediately press-hold Command + R simultaneously.

Step 2: Shortly, you will be booted in the Recovery Mode. Here, you are presented with four options to troubleshoot your Mac. Disk Utility is one of those four options; click Disk Utility to launch.

Step 3: Choose your start-up disk (Macintosh HD) and run First Aid to repair cryptic disk errors on Mac hard drive.

There will be two possible outcomes after the Disk Utility is done repairing the failing Mac drive:

i) Mac start-up disk is repaired successfully with the Disk Utility: When the Disk Utility shows you the output that it has repaired the corrupt disk successfully then you can log-out from the recovery partition and boot into the desktop as you would usually do.

ii) Disk Utility Can’t Repair the Corrupt Start-up Disk Drive!: There are several limitations of the Disk Utility itself such as it can’t repair a corrupt partition map. Also, it can’t repair advance disk errors such as Invalid-B Tree Node. To Repair Invalid B Tree Node on a start-up disk it is required to back up the Mac drive and erase it with a new partition scheme.

Regards,

Adrian

Did you erase the whole physical drive so you would only have a single "Macintosh HD" volume? You may need to click on "View" within Disk Utility and select "Show All Devices" before the physical drive will show up in the left pane of Disk Utility.

It sounds like you may have a failing hard drive. Depending on the age of the iMac, you can try running the Apple Diagnostics. If you can boot macOS (internal or externally), then you can run DriveDX to check the health of the hard drive.

If none of these are options, then create a bootable Knoppix Linux USB drive using Etcher (Mac/Windows/Linux). Option Boot the Knoppix USB drive and select the orange icon labeled "EFI". At the Knoppix desktop, click on the "Start" menu on the bottom left of the Taskbar and navigate to "System Tools --> GSmartControl". Within the GSmartControl app, double-click on the iMacs drive icon which will provide you with the health information and attributes for the drive.

Post the report here using the "Additional Text" icon which looks like a piece of paper. If you have multiple drives in the iMac, then post a report for each one.