Keys stand for power and access. To lose one's keys in a dream is to be out of control or lack the means of access. It may symbolize that you feel unable to acquire what is needed to complete a task or obtain access to persons or knowledge.
To find your own keys is to assert your own power in a given situation. You have the ability to be "captain of your destiny," so to speak.
What is most interesting is to find a key that previously had no meaning for you. This is especially important when the key has no direct use, but "feels" as if it might be important. In a dream like this, you are probably searching for options to identify new potential within yourself or in relationship to others.
Who was with you when you found the key and with whom did you share the discovery in your dream? There will be numerous clues in the answers to these two questions.