In future, don’t mess about with things you don’t understand…
For now, you will need to re-build the HDD, which is a multi-partition, Linux-based file system, which includes the MyCloud operating system. The MyCloud is a linux-based file server, not a simple HDD.
See the following guides for ‘unbricking’ or replacing the HDD. You will need to determine what firmware you need to install on it. If the serial number ends in -00 (or possibly -01), it’s a Gen1/v4 firmware. If it ends in -10, it’s a Gen2/v2 firmware. You may have to search the forum for Gen2 unbricking guides.
