Can you try it on another PC? You do not say what model your external drive is. If it is a small portable like this :Seagatethen you will have problems removing the hard-drive. If the hard-drive has been dropped it might be just the caddy is damaged.If you can remove the hard-drive you could either buy a new caddy or connect it to your PC using a simple connector.Connect Please post model of Seagate drive.
iMac Pro review