I read this and think it may be the issue but I don't really understand it... http://knowledge.seagate.com/articles/en_US/FAQ/006125en?language=en_US
Also this may have something to do with it...
https://community.wd.com/t/seagate-3tb-hard-drive-not-recognized/31916/18
There seems to be an explanation for it and perhaps a remedy, but I need someone to explain it to me in plain English if possible.
Cheers :)