[Roy Dennis]

If as you say the file path list shows as a blank list, not as shown in my previous attachment.
While it is showing blank press the rebuild database button and it should very quickly come up with something like no songs in database, which will mean it has created an empty database. This is a good thing at this point because when you start the next procedure it wont be creating duplicate entries.

Once it reports no songs in database Use the ADD songs button and brows to a folder containing your songs on your C drive, make sure to go right into the folder so that it shows a list of the songs then press select. It should then add all the songs in that folder to the list and Database.
After that it should show that folder path in the List of folders. if not something else is wrong.
Assuming that folder listed OK either add each folder one at a time or use the Add Folders/Subfolders button to auto Add all folders in the in the tree below that starting folder. it should build the database as each folder is indexed.

Now regarding your E drive providing that contains unique songs that are not copies or backup files continue to add those folders.
If the files on the E Drive are just Backup files then do not index them.

Regarding quickly changing to a backup drive.
All your songs would have to be on a single drive
it would be best to only load your songs onto your E drive only.
Build your database to your E drive only no songs on C.

Then copy the files on the E Drive to Your USB drive making it an exact replica of the E drive so that the file paths are the same Except for the starting volume letter.

Now in the event of a failure of your E drive you could go into Disc management and Change the File path Of your E Drive To anything else available, then Plug in your USB drive and go back into Disc management and set that to E drive, that would then act the same as your E Drive.

Alternately you can Just plug the USB drive in, Open Hoster Edit dialog and select My drive has changed and choose the drive letter of your USB.
I have not used this lst method not sure if it rebuilds database or works instantly but know others who have used it so know it works.