On systems running older operating systems versions you will have to start a browser and load a website (any website) to force a hotspot portal to appear. This even applies to smart phones running an old OS. A modern OS loads a specific website automatically when connecting to a WLAN, this technique is called »Network Awareness Test«.

A portal never appears by itself, it always needs a request for a web page to be able to redirect the browser to the portal instead, either initiated by the user or by the OS.