Hen not sitting on eggs anymore
She may just be done brooding. Three weeks is how long it takes eggs to hatch, so now that it's been four weeks, she may just be done with it. Her body knows that it's time to give up because her eggs aren't going to hatch and being broody is hard on a hen. She might even start laying in the nest and pooping on the eggs if you keep her in the crate with them now that she doesn't want to hatch anymore.
Your best bet, if you really want them to hatch, is to buy or borrow an incubator and use that. Unless she sits on them all the time except to take a short break once a day, they will never make it to hatch.
Unless you really want to raise the chicks yourself, I'd be inclined to throw out the eggs rather than incubate them. If you do decide to incubate them, time is critical as the hen is no longer incubating them. I wouldn't want them to cool down for more than 12 hours at the most.
I feel bad, but I think I'm just gonna give up. The only reason I got the eggs was for her to hatch them. I don't have an incubator, and don't have time to learn, and do it myself. Maybe next time, I'll give her eggs right away instead of waiting too long. Lesson learned.
Don't beat yourself up. So much of chicken-keeping is a learning experience. You'll be well-prepared when the time is right.