Connecting external HD

Hello stevekerry,

Thank you for reaching out to Apple Support Communities.

Let's review all of these steps to see if your external drive works again:

"If a USB device doesn’t work with Mac

If a USB device isn’t working properly, make sure it’s connected to your computer correctly, is plugged into a power outlet if it has a power cord, and has any necessary software installed.

• Check the power, port, and cable connections: Make sure the USB device is turned on and its cables are properly connected. If your computer has more than one USB port , switch the device’s cable to another port. If you still can’t use the device, contact the manufacturer for more information.
• If you can use the device after switching ports, connect another device to the first port. If you can’t use this device, shut down the computer and unplug it from the power outlet. Wait about a minute, then plug it back into the power outlet and start up your computer.
• If you still can’t use a device with the port, your computer may need to be serviced. See Find out how to service or repair your Mac.
• Check for missing software: Make sure you installed the latest software for your device. Visit the manufacturer’s website for any updates.
• Check the USB hub: If the device is connected to a USB hub, make sure the device and the hub are the same speed. Connect USB 3.0 SuperSpeed devices to a USB 3.0 SuperSpeed HUB, USB 2.0 Hi-Speed devices to a USB 2.0 Hi-Speed hub, and so on.
• If the device doesn’t have a power cord and is plugged into another USB device that doesn’t have a power cord: Try plugging the device directly into your computer’s USB port  or into a USB device that does have a power cord. You might need to disconnect and reconnect the other device as well, if it has stopped responding.
• If you have many devices connected to your Mac: Disconnect all USB devices except the device you’re testing, an Apple keyboard, and an Apple mouse. Make sure that the device is connected directly to the computer, and that any hubs or extension cables are disconnected. If you can use the device now, the problem may be with one of the other USB devices or hubs you had connected to your computer. Try reconnecting them, one by one, to your computer. When you find the device causing the problem, review its documentation for further troubleshooting steps.
• Verify that the device appears in System Information: On your Mac, press and hold the Option key, then choose Apple menu  > System Information.
• In the window that appears, see if the USB device is listed below Hardware in the list on the left. If the device appears but does not work, review the device’s documentation for further troubleshooting steps.
• Reopen apps: Quit and reopen any apps that use the device.
• Restart your Mac: Choose Apple menu  > Restart."

Additional details can be found here: If a USB device doesn’t work with Mac

If the issue persists, can you provide a few more details? Does your drive work with another computer? Do other USB devices work on your Mac? This will help us further isolate the issue.

Cheers!

If you wont't attach the drives, they are useless.

Hard drives are like all other pieces of tech and sometimes they simply err. When that happens, you can either trash them and buy replacements or try and fix the problem.

I suggest you attached the faulting drives directly, open Disk Utility and run 1st Aid. Depending on what happens with that you may need to erase and reformat them.

The problem with hubs and docks is they sometimes tend to complicate attaching external devices. You apparently have opposite problem which tends to make me think the drives have either faulted or failed. If the drives are five years old or older, they need to be replaced anyway. That may be true even if less than five years old.