Why does my LG BD player only plays DVDs?

Because your question lacks details, I have to ask you dumb questions, like, is it hooked up to an HDTV? It probably is. Bluray players require updates in order for them to recognize the latest Bluray disc releases, I think. Even if that last sentence is inaccurate, they still do need to be updated from time to time. Go to the LG website and look for an update-download for your model.