1. Describe the problem exactly. Is it just the iPad mini not connecting to the server (e.g. an error of some sort) or is "Get books > OPDS auto or calibre server" not finding the server at all?
2. Can you access the Calibre server on the PC it's running from?
On a web browser, type the ff in the address bar:
http://localhost:8080/
3. Can you access the Calibre server from another computer?
(you can find the IP address in Calibre's Preferences > Sharing over the net)
http://ipaddress:8080/
4. Can you access the Calibre server using Safari on the iPad mini?
(same as #3)