Cannot enable secure connection

Using 2.1.2, In the General:Settings page (?dispatch=settings.manage) each time I select the checkboxes:-



Enable secure connection at checkout (SSL certificate is required to be installed on your server)



Enable secure connection in the administration panel (SSL certificate is required to be installed on your server)



Enable secure connection for authentication, profile and orders pages (SSL certificate is required to be installed on your server)



And press save, the page refreshes without the boxes being saved.



Beyond this, despite having an SSL installed, I cannot get the checkout pages to work under HTTPS



Any ideas?



Thx



Alick