Do a subforum search for “unbrick”, there are numerous past discussions with a variety of ways to unbrick/reformat the My Cloud hard drive. Note because the My Cloud drive uses Linux, it is often best to use a Linux Live CD/boot CD and NOT Windows to perform the unbrick procedure on the drive when it has been removed from the My Cloud enclosure. Windows doesn’t have the necessary drivers to read/write to Linux drive format used by the My Cloud. One can try using third party Linux drivers for Windows but its often just easier to use a Linux boot CD.
Fox_exe’s unbricking steps, make sure to choose the correct My Cloud unit/firmware version:
https://drive.google.com/drive/folders/0B_6OlQ_H0PxVZTBtM3EyRVhDVms
Unbrick:
https://community.wd.com/search?q=unbrick%20category%3A105
https://community.wd.com/t/guide-how-to-unbrick-your-2tb-3tb-4tb-my-cloud/93336
Try Linux Ubuntu:
https://www.ubuntu.com/download/desktop/try-ubuntu-before-you-install
