Why Wont My Parakeets Mate Or Go Near Their Nest Box?

My Keets are about 2-3 years old and the male has a light blue cere and the female has a brown crusty cere during certain times of the year. i have put a nesting box on the outside for about 4 months now with some string and wood shavings, at first the female (Jenna) would poke around inside but now she doesnt go near it. Jenna now pecks at the male (Tommy) whenever he tries to mount her. but they preen and are close to each other . finally they both have really bonded and lokk like the love eachother because Tommy seems like he ant be without Jenna, and the play with the nestin together but not make a nest. please answer and please be a correct answer i really need to know! Thank you