Hello Sir & welcome to JustAnswer. I am happy to answer your question.
Dear sir, If your camera not turning on with battery & not even with Power supply then its a internal power supply unit fault.
For few reason this problem started.
1. The connectivity cable from camera to Circuit board damaged or disconnected.
2. The power supply transformer stop working & need to replacement.
3. turn on button connection may disconnected. After visual checking by the technician is possible to say which part is faulty.
For the confirmation you need to visit a camera repair store. Without visual survey technician can't confirm you which one of them is faulty. Thank you.
i am not and expert so all the things you said didnt make any since by the way im a woman
Ok Madam, I understand. In simple word this is camera electrical fault. For the solution you need to visit Nikon Camera service center . If your camera still cover the warranty then you can get a free service. If you want to know your nearest camera service center address then please let me know your city name or location. Thank you.