Eggs take 21 days or so to incubate. If the eggs have been under her for 4 weeks, they aren't going to hatch (assuming we are talking chicken).
If eggs have been added to the nest over time, it is anyone's guess.
I would candle the eggs (there is a great article on that here on BYC) http://www.backyardchickens.com/t/261876/chicks-are-here-egg-candling-pics-progression-though-incubation is the link. If they have a red line around them, they are dead (blood line). If they are clear they are unfertilized or brand new. You are looking for development in the egg.
Pitch any that smell (very carefully they are stink bombs) or are obviously dead or not developing.
Now look for movement in the remaining eggs.