U.N. success stories
You say that the UN talks but never solves anything? If so, then there are a number of things to point to that the UN has done a pretty good job of. I won't waste the search-time unless you persist, though.
I won't make you cough up links. Just name nations and/or conflicts where the U.N. has triumphed in the area of stopping a war, preventing a massacre, or creating a stable democracy. Remember, I'm talking geopolitics, not humanitarian work.
Korea might be one. At least the fall of South Korea was prevented. Nothing else is immediately coming to mind.