Parakeets Wont Mate

Question
Okay,

So I have two parakeets: A male and a female who are both at least two years old. They absolutely LOVE each other. When I had my other three parakeets, the male wouldn't let the other males get near her. Right now, the females cere is a dark crusty brown (it has actually been like that for a couple of months). I have been giving them vitamens, cuttlebone, mineral block, etc... However, they just won't mate! Or should I say the female won't. The female always screeches at Petree (the male) and then goes back to preening him the next second. Do you think it's because she is very timid and untame, making her very uncomfortable around humans? Oh yeah, and I have provided them with a nesting box, but it could only be inserted on the bottom of the cage, because I wanted it to be on the outside with easier access. I just want to know if it's something that I'm doing, or are they just not wanting to mate for some other reason. I did hear that parakeets wont mate without colony breeding. Thanks for your time.

-Yana

Answer
It sounds to me like your doing everything on your part you can do correctly. However. The first and foremost thing you need when breeding parakeets is patience. PATIENCE PATIENCE. They will mate when they are ready, and it will happen, because every keet has the instinct to recreate. Just wait and everything when happen when they are ready, sometimes it takes weeks, sometimes months, sometimes years, its up to the bird.

Hope I Helped!