Hard Drive Mounting Issues

Some WD models do not work on Macs, but WD won't tell you which do work. But they are all going to get to you formatted for Windows. Before you can use them you need to partition and format them. If the drive is already formatted NTFS, then to reformat you will need to use Windows' disk utility to change the format to FAT32. You may be able to do this on your Mac but it may take several tries.

This process will install the original version of macOS that came pre-installed on your Mac when it was new. After it finishes you can upgrade it further to High Sierra - How to download macOS High Sierra.

Internet/Network Recovery of El Capitan or Later on a Clean Disk

If possible back up your files before proceeding.

1. Restart the computer. Immediately after the chime hold down the (Command-Option-Shift-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the drive (usually, the out-dented entry) from the side list.
5. Click on the Erase tab in Disk Utility's main window. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
8. Click on the Apply button, then click on the Done button when it activates.
9. Quit Disk Utility and return to the Utility Menu.
10. Select Reinstall OS X and click on the Continue button.

Note:

1. To install the version of OS X that was currently installed use Command-Option-R.

2. To install the original factory version when the computer was new use Command-Option-Shift-R.

in High Sierra, The default Volume-view is completely useless, and far as I can tell.

you MUST change the default in Disk Utility or Device-View.

elect the drive by Hardware-name, and ERASE.

Open the Terminal in the Utilities’ folder. At the command line enter or paste:

diskutil list

Press Return.

The output will look something like this taken from my machine:

Stevens-iMac:~ skapplin$ diskutil list

/dev/disk0 (internal):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme 251.0 GB disk0

1: EFI EFI 314.6 MB disk0s1

2: Apple_APFS Container disk1 250.7 GB disk0s2

/dev/disk1 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +250.7 GB disk1

Physical Store disk0s2

1: APFS Volume Macintosh HD 69.4 GB disk1s1

2: APFS Volume Preboot 45.0 MB disk1s2

3: APFS Volume Recovery 512.5 MB disk1s3

4: APFS Volume VM 2.1 GB disk1s4

/dev/disk2 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *960.2 GB disk2

1: EFI EFI 209.7 MB disk2s1

2: Apple_APFS Container disk4 480.1 GB disk2s2

3: Apple_HFS Sierra 479.1 GB disk2s3

4: Apple_Boot Recovery HD 650.0 MB disk2s4

Identify which disk is your startup disk. This would be a physical disk such as /dev/disk2 shown above. In Terminal's command line enter or paste the following:

diskutil mountDisk /dev/disk2

Press Return.

Check the Desktop to see if the disk is now mounted.

Did you also replace the drive cable?

Litmus test: Does the drive work in an External enclosure, but not inside the Mac ??

Can you take snapshots of your Disk Utility's windows so we can get a better idea of what's going on? Have you tested using the Mount button in Disk Utility's toolbar?

I copied all of my files onto an external hard drive.

Then you DO have an external enclosure, it would just be some work to put a different drive in it.

OK, thanks. The disk is formatted but not mounted. Did you try using the Mount button?

Install Lion Through Yosemite from Scratch

1. Open Disk Utility in the Utilities’ folder if it isn't open already.
2. After Disk Utility loads select the disk2s2 volume (this is the indented entry shown selected in the last image you posted. Click on the Erase button in Disk Utility's main window.
3. Set the Format type to Mac OS Extended (Journaled.) Click on the Apply button
4. When the process has completed quit Disk Utility, and return to the Utility Menu.
5. Select Install OS X and click on the Continue button.

This should fix things for you.