Try going to Start; right click on Computer; click on Manage; click on Disk Management under Storage on the left and your drive should show up with a blue line. Right click on the blue line and select Change Drive Letter and Paths. This will allow you to choose a drive letter and the external HDD should then show up in Windows Explorer.
I am having the same original problem with a thumb drive I regularly use on this computer. Changing the drive letter and path name doesn't seem to help my situation. I have 1 internal HDD that is labeled Disk 0 and has a status of "online." My thumb drive is labeled as Disk 1 and has a status of "no media." Any thoughts?