You can put the hard drive from the My Cloud into any SATA to USB dock / enclosure and use a Linux OS to unbrick. There are various Linux boot discs one can download and burn to a CD/DVD/USB flash drive and boot the computer with that Linux boot disc to unbrick the My Cloud drive. Unbricking will require some knowledge of how to use the command line terminal in Linux and commands that get issued via that terminal. And opening the My Cloud enclosure will in all likelihood void the device warrantee.
There is also the following option one person claims to have used that didn’t require opening the My Cloud enclosure:
