If there is a compatibility problem between the pair, you might never see eggs. Another strong possibility is that the female is laying eggs, but one or both of the birds are destroying them. Some pairs that break their eggs are not content until they have pulverized the shell to the point that you find no broken shell in the box upon gross examination. Many times, finite inspection of the nesting material will reveal the pulverized shells. The last major possibility is that there is something physically wrong with either the male or the female.
Some males never mature sexually, even though they develop mature plumage.
Many males in this condition will never commence courtship behavior. Those that do will not have their females laying fertile eggs. The female, as well, might be the problem. If these problems are at the end of the process, they can result in egg-binding and associated problems. If the problems are at the beginning, then you might never know that anything was wrong.