What type of incubator are you using? What humidity and temperature is it kept at? A faulty incubator can sometimes cause poor hatches, though I would expect that if that were the case, your broody hen hatch would have been successful.
Otherwise, the best conclusion I have is that your eggs are not fertile. How do you know they are fertile when you crack them open? A fertile egg that has been incubated (even in less than perfect conditions) should show some blood vessel development. If they don't, then they are likely not fertile.
Some people have success telling fertility by looking at the shape of the white blastoderm on the yolk, but this can be somewhat unreliable. In theory, though, a infertile egg's blastoderm will be a solid white color and irregular in shape. On the other hand, a fertile egg's blastoderm will have concentric rings (creating a "bulls-eye") and will be rather round. Did you see the bulls-eye in your "fertile" incubated eggs?
It is also possible that your eggs were fertile, but were killed early on. Did you store the eggs before incubating them or putting them beneath the broody hen? If you did, at what temperatures and humidity were they stored, and for how long? Extreme temperatures and long storage (2+ weeks) can result in lowered egg hatchability.
I'm sorry about your failed hatches. Hopefully, we can find out what was wrong!
