Which model of kindle is this that you have?
Confirm that you have the correct password, if it is coming back as incorrect it most likely is not correct. If you are positive you have the correct password ***** are typing it correctly try the following.
Press and hold the Power button for seven seconds until the Power dialog box appears, and then tap Screen Off. Turn off your router and/or modem for 30 seconds, and then turn them back on. After your router and/or modem restarts, press and hold the Power button on your Kindle until it turns on, and then try to connect to your Wi-Fi network again.
Make sure you also follow these instructions so you are choosing the correct network, click the link to view step by step