HDD does not show up in File Manager

This Plugable unit worked with my system. I just plugged it into the same USB port it used before and I cannot get a HDD letter to show up in File Manager. The Devise shows up in Device Manager and reports “working properly”.
The unit does work when plugged into my laptop.
Any ideas for me?

[running windows 8.1 with two external hard drive and 2 internal hard drives - al of which are functioning. Also tried several USB ports both 2.0 and 3.0]