WD sent me the following information. My WDmycloud seems incapable of a hard reset however, so will be replying to them Will let you know if I have any more luck.
"Thank you for contacting Western Digital Customer Service and Support. My name is [Deleted].
I apologize for the inconvenience you are experiencing with your device.
Could you please let me know what operating system do you have?
If you have Windows, please check if you can access the WD My Cloud by using the WD Discovery utility. You can find the instructions how to do it on the link below:
If you cannot access the data by using the “Map network drive” function, but you can see the unit listed, please access the Dashboard of the My Cloud:
In the Dashboard, please try to restore the operating system of the device. You can do this by following the instructions on the link below:
From the table, please select the option “WD My Cloud System Only Restore”. This will only restore the settings and the operating system of the device, without deleting the data on it.
If the My Cloud does not appear in the WD Discovery, or you have a Mac, please perform the system restore of the My Cloud manually. It is possible to perform a System Only factory restore physically. At the same time as the power adapter is plugged to the WD My Cloud device, press and hold the Reset button on the back of the device for about 40 seconds. This process will not touch the data on the network drive.
If you have any further questions, please reply to this email and we will be happy to assist you further."