Possibly eggbound? There are ways to check. I've had to violate my little girls to help a couple along before. Not something you want to do if you don't have to. Risk shattering a shell. There are a few experts on here that will be able to better walk you through the procedure. I had on-line researched it when I had this problem and had at the time found some good sites to walk me through it. You can do a warm bath to start which is what I always do first. This helps ease the vent and the hen. Both of mine were really good about the bath. Chloe went right to sleep on me. Warm heating pad on the belly helps too. If this doesn't work though, then its gloving up, lubing the finger and checking inside the vent. I'll let the pro's here handle that part of explaining though. I know someone else on here had the same problem recently and another member had done a great job of explaining the procedure.
There are ways you can tell if a hen is egg bound. Usually a hen having problems will make noises and will keep trying to nest to lay but nothing comes out. The action will be continuous. She will not let up. If you check the hens vent, sometimes you can she a gooey mess that can be either white or yellowish. It's usually is the tell tale sound.
If you think a hen is bound, put her by herself. Best place is a warm place but not a hot one. You can try placing her in warm water as that will help her relax her muscles. Soak her for about 10 minutes. It might take several soaks or you might get lucky the first soak. While soaking her, gently massage her side around the vent. Gently move your hand in a downward motion towards the vent, can help stimulate the egg inside to move down towards the vent. Another is if you take your finger and gentle massage the vent opening. Just you finger tip and a gentle push on the vent again can trigger the hens to bear down and push.
I have had to remove an egg from inside the hen. It is as 7chicks has said, it should only be done as a last resort because you can kill the hen if it isn't done properly. I only do it as a last resort when I know if I don't do a thing the hen will die anyway. Thankfully, the warm water treatment often works and the actually going in and getting that egg is a last resort.