Is it personal stuff he doesn't want to talk about or just talk in general? Maybe make a game out of it? Write down a bunch of questions on little pieces of paper, some personal and just some general and put them in a container. The next time you two are together take turns picking out a question and discuss each others answers.

Maybe try doing on interactive sport or game together, one that you have to communicate to do.

Its possible you have nothing in common or have everything in common.