Are you setting the “new from” and “new to” dates in the backend for the products? The new products block is not “recently added” products, but rather products that have to be defined as new.
I’m having this same problem.
I’ve inputted one category, and one product in that category to test.
I marked both ENABLED, and the product as NEW.
Nothing shows on my homepage.
I installed the MODERN theme, and have posted an issue with getting it to work also in the Modern theme Documentation thread.