Try putting a fake egg in the box. It might help. I was having a problem with my new pullets laying eggs all over the floor. I put a fake one in and they started laying in the box, but as soon as I took out the fake egg, they laid on the floor again. I guess I have to leave the fake egg in awhile longer. Good luck!
out of our 19 hens 6 lay in the coop in the nest boxes, or on the floor, then about 8 lay in the garage, the others lay whereever they feel like it and that could be under the car, in the wood pile, in the bushes, on the patio table....or places we havent found yet. We have given up trying to get them to lay in the boxes. We just go on egg hunts every day.
Birds that are starting to lay haven't learned the body clues yet to know when it's "time" to hit a box. I understand from these boards that it's pretty common for young pullets to lay on roosting bars until the get the hang of it.