Hi Keith,You should see the rear view by clicking the Rear View button (next to the Front View button) in the Tools toolbar.
Can you confirm that you started the drawing based on the Panel Layout template? It is the template that determines which views are available and, in Panel Layouts, it is normal behavior for High Detail to be disabled (it is the default view and there is no 'Low Detail' view in this environment). The template and current layer are shown in the middle of the Status Bar at the bottom of the screen e.g. "Panel Layout : Parts"
If you continue to experience problems, please attach a .zip of the .S01 drawing to a post to this forum and we will be ahppy to check it out.