Passive: I was sent to the principal’s office. [The subject of the sentence is “I,” and being sent is what’s done to the subject.]
Active: Miss Hegel sent me to the principal’s office. [The subject—Miss Hegel—is doing the sending.]
Passive: The walls are being painted yellow. [The subject is “walls,” and the painting is being done to them.]
Active: The boys are painting the walls yellow. [The subject is “boys,” and they are doing the painting.]
Passive: You will be given an opportunity to respond. [The subject is “you,” and the giving is being done to you.]
Active: The moderator will give you an opportunity to respond. [The subject is “moderator,” and he or she is doing the giving.]
Passive: The system has been shut down. [“System” is the subject, and shutting down is being done to it.]
Active: The system has shut itself down. [The system did the shutting. Also active: The operator shut the system down.]
Passive: She would have been fired if she had been caught.
Active: The boss would have fired her if he had caught her.
Notice that when you go from passive to active you are changing the subject of the sentence. When it doesn’t make sense to change the subject, that’s when you want to keep it passive. Who wouldn’t normally say “I was born”? You make it active—“My mother bore me”—only when there is a need to focus on the matter of giving birth.
Auxiliary verbs have nothing to do with it.