My budgies wont breed?

i bought 2 budgies as adults almost 3 years ago as adults n i was never interested in breeding but ther atleast 3 years old n if i dont breed them this year it will be my last chance bcuz next year they will be too old but they dont seem interested to breed.the hen is a violet budgie wich is not that common thats another reason y i want to breed them. the hoops(hen) used to go in the nest box but lately she dosnt n if i put shreded paper is the box she throws it all out.sometimes, but only RARELY i see the mate sing a bob his head n kiss.i tried misting them weekly n the have a mineral block n if they start breeding i will buy a cuttle bone(forgot to get one). i have no other budgies n ther cage is 30x17x16 inches n ther nest box is 6 in long its been ther for 3 years but they never mated. r they a bonded pair? n at the pet shop hoops was kissing a green male n all the males wer green n i dont think yoyo(male) is the one i saw her kissing at the shop will that affect the breeding?