Can be WPK problem. Some kindles can only authenticate on WEP. So if the password on your wifi is not WEP, maybe consider changing that. Then try again. Ref: https://www.youtube.com/watch?v=LDGq9eHkUrA
There should be a password on the back of your router and that should be able to get you into your wifi, if not you can reset the router by pushing a little reset button that can be found on the router, on the back, and this will reset the router to default factory settings, which will then make the password work
Can be WPK problem. Some kindles can only authenticate on WEP. So if the password on your wifi is not WEP, maybe consider changing that. Then try again. Ref: https://www.youtube.com/watch?v=LDGq9eHkUrA