Your cockatiels bird lays eggs but never hatch but you dont know why?

First of all determine if the egg could be fertile. (like if there is a male and female together) Cockatiels are notorious for excessive egg laying. Make sure she is getting plenty of calcium. (Either a cuttlebone, grit, or something along those lines. keep her in an area that has more activity. Those are just a couple suggestions to get you started.