IMac won’t boot. Did I kill it?

DeweesL wrote:

It makes the start up noise then it pauses for a few moments before it shows an icon of a folder with a question mark inside.

Make sure to use a wired USB keyboard to access the special startup keys since a wireless keyboard won't go ready soon enough. If the iMac cannot connect to the Internet when attempting to boot into Internet Recovery Mode, then it will attempt to boot from any other bootable drive....if unsuccessful in finding any bootable drive you will get the blinking folder with question mark.

How did you attempt to create the bootable macOS USB installer? Here is an Apple article with instructions, but it requires access to another Qualifying Mac:

https://support.apple.com/HT201372

A Qualifying Mac is one which is compatible with the OS installer you are trying to create (the Qualifying Mac can be running any OS though). See this article for showing which versions of macOS are compatible with various Apple hardware:

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

If you don't have access to a Qualifying Mac, then you can try using DiskMaker X on any Mac which is compatible with the DiskMaker X software.

You need to use a wired USB keyboard to access the Mac's special startup keys in order to Option Boot the iMac to access the bootable USB installer.

They may not even work on it.

Which of the 3 methods did you use?

Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following combinations on your keyboard. Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later… How to reinstall macOS - Apple Support

Command (⌘)-R

Install the latest macOS that was installed on your Mac.

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

Shift-Option-⌘-R

Install the macOS that came with your Mac, or the closest version still available.

2. Decide whether to erase (format) your disk

If you need to erase your disk before installing macOS, select Disk Utility from the Utilities window, then click Continue. You probably don't need to erase, unless you're selling or giving away your Mac or have an issue that requires you to erase. Learn more about when and how to erase.

3. Install macOS

After starting up from macOS Recovery, follow these steps to install macOS:

1. Choose Reinstall macOS (or Reinstall OS X) from the Utilities window.
2. Click Continue, then follow the onscreen instructions to choose your disk and begin installation.
3. If the installer asks to unlock your disk, enter the password you use to log in to your Mac. If it doesn't see your disk, or it says that it can't install on your computer or volume, you might need to erase your disk. 

1. Please allow installation to complete without putting your Mac to sleep or closing its lid. During installation, your Mac might restart and show a progress bar several times, and the screen might be empty for minutes at a time.

If your Mac restarts to a setup assistant, but you're selling or giving it away, press Command-Q to quit the assistant without completing setup. Then click Shut Down. When the new owner starts up the Mac, they can use their own information to complete setup.

If you never installed macOS Sierra 10.12.4

If macOS Sierra 10.12.4 or later was never installed on your Mac, macOS Recovery works differently:

• Command-R is still the recommended way to start up from macOS Recovery. This combination makes sure that the installation isn't associated with your Apple ID, which is important if you're selling or giving away your Mac.
• Option-Command-R installs the macOS that came with your Mac, or the closest version still available.
• Shift-Option-Command-R isn't available.

How to reinstall macOS - Apple Support 

Yes, chance.

Also might install an OS to an external drive.

1. Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following combinations on your keyboard. Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later… How to reinstall macOS - Apple Support

Command (⌘)-R

Install the latest macOS that was installed on your Mac.

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

Shift-Option-⌘-R

Install the macOS that came with your Mac, or the closest version still available.

DeweesL Said:

"IMac won’t boot. Did I kill it?: I was attempting to reset my iMac to give it to someone else, but after erasing the drive, I couldn’t get it to reinstall the OS (High Sierra). So I created a USB boot disk but couldn’t get it to boot off the USB.[...]"

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For reference...

Troubleshooting MacBook Pro Power:

As for replacing that battery, that may not be necessary. Try troubleshooting it.

A. Black Mac Screen:

Go Here: If your Mac doesn't Turn On or Start Up - Apple Support

Applies to Intel-Based Macs: Try Resetting the SMC and NVRAM, but this time, using an external keyboard. Connect an external monitor and see if you get an output.

B. Mac Power Issues:

Try a New Charger:

If it is currently charging from a charger, then use a new charger:

• Power & Cables - Mac Accessories - Apple - Select "Mac Compatibility" on the left
• Find the right power adapter and cable for your Mac notebook - Apple Support

C. A Few Links to Refer to Power:

• If your Mac doesn't Turn On - Apple Support

• How to Turn your Mac On or Off - Apple Support

• About Mac Notebook Batteries - Apple Support

• Charge the MacBook Pro Battery - Apple Support

• If your Mac Battery won't Charge - Apple Support

Sounds like it's a goner, but one last long shot...

1.. Shut the machine down.

2.. UNPLUG the power lead to the computer and any peripheral devices.

3.. leave it for 10 minutes.

4.. Hold power Button in for 10 seconds

5.. Connect everything back up and restart. 

Is it starting at all, likeany lights, sound, action?

Does holding Option key at startup show any boot choices?

Last MacOS available on DVD was 10.5.8

Great outlook my friend, best of luck! :)