Hello my name is sean and i'm going to help you with this today,likely we will need to factory reset the device since there is no "back door" approach we can take, if your password is no longer working, likely someone else has changed your password. Ensure that you are entering it with proper capitalization too of course... can you tell me which type of Kindle this is?
Is this the kindle 1, 2 3, dx, or fire?
I will happily walk you through the steps but if I should happen to miss you, please feel free to check this out : http://resetkindle.info/ and according to which one you have, you can follow the instructions for it
You may try typing "resetmykindle" as a password too