Drive not working PLEASE HELP!

A client has purchased this drive and after a period realised it stopped working. The drive would boot using the blue light then go to a steady yellow light where it would stay consistently even on rebooting would do the same process. I took a look at one of the manuals and it stated that the yellow light meant it was loading the OS. However this takes days still nothing. I then took the hard drive out of the casing and connected it to an enclosure. What I discovered was that the whole disk was in RAW file system and nothing could be accessed which lead me to believe that that was the reason no OS could load. With no other option I formatted the drive now I have a working drive that can be accessed however it would not work in the NAS casing because it does not have this “OS”

My question is where can I obtain this “OS” and what steps I need to follow to have this drive back up and running and operating as a NAS once more.

Hi thankyou for your suggestion however this did not work I received an email from with the following.