Are you running Linux or do you have a third party Windows driver installed to read Linux drives?
The My Cloud drive is formatted for Linux. Without a third party driver in Windows you generally will not be able to access it. If possible use a Linux Live CD/Boot CD to run Linux on your PC to access the My Cloud Hard drive.when removed and attached via a SATA to USB adapter to your PC.
DO NOT attempt to format or partition the drive from within Windows without using a Linux driver/software. Doing so will potentially erase the data on the drive.
