Download Recover My Files from
www.recovermyfiles.com onto your C: drive.
Run the program and select "Complete Format Recover".
In the drive selection window, select the "physical drive" (the one that is closest in size to your problem external drive).
In the file type selection window, use only the default selected file types, but also add the Turbo Tax file type to the list to recover.
Run this search. It will take a number of hours, but at the end you should see you full file and folder structure in "Folder View" of the results screen.
Preview the files here (no preview for turbo tax) to make sure the data found is valid, and then purchase a key to save the important files back to C: drive.
Good luck.