if this is your first hatch, don't get discouraged. several things can go wrong.
have you calibrated your thermometer and hygrometer? if your temp is a degree low, something might hatch. it will be late. if nothing by day 23 its probably a total loss.
so many people are running humidity to high, i find mine works best (in southern ohio) if i run my humidity at 45% until day 18 then raise it to 55-60% through hatch.
if your using a Styrofoam incubator, you cant leave it closed for hatch. you will have to open it and add water. do this quickly.
also, if you start a new batch, open your incubator 15 mins a day and let the eggs cool a little. this simulates the hen getting up to eat, drink and do her business. also if you have a power outage your eggs will handle it a bit better.