It should only be approx 19-22 days for chicken to hatch. If older than 25 days, the eggs won't hatch for sure. Part of the reason can be no fertiled (no mating, hen too old or rooster too old), wrong setting (over heat in summer, or naked hen cannot cover enough, or just poor method of covering the eggs from a hen). If none hatched then maybe the eggs are not fertiled, my best guess. Take a look at the nest to see if eggs are still in there; sometimes rodents, snakes, varmints took the eggs and the hen still tries to set.
For old/overdue eggs, you need to throw the eggs away before they popped by themselves with stinky smell. Before you throw them away, you may double check to see if any baby inside. This is very easy. Take them inside your restroom at night, with the light off, use a flash light placed at 1 side of the egg and you observing the egg from the other side. Clear color means no chick. And big black cloud means .. baby. With the one with baby inside, you may want to put back in the nest for a couple extra days of setting.
Good luck.
