Is it just Lego PotC? How long's it been happening? How old is your Wii
In my experience, the Wii freezing in how you've described (it's happened to me a few times) is an internal error of sorts, characterized by the console being unresponsive to any and all input. Could be a problem with the game itself, be it the disc is improperly made, or scratched. On the contrary, the Wii could be malfunctioning from age, or it isn't programmed as good as it should be.