First I want you make sure you are using correct WiFi password. If it still not connecting, then we have to make some adjustments to router to get it connection.
Follow the steps below to get the WiFI password ***** your computer.
Click on the network/wireless icon at the bottom right of the screen (left to the clock)
From the list of networks, right-click on your wireless network name and click on Properties.
Then click on the Security tab.
Then click the box at Show characters.
This will show the password ***** the text box. Use that password ***** connect your Kindle to your network.
Another way is, press Windows and R keys at same time and this will bring Run window. Type ncpa.cpl and press enter. You will see the WiFi network adapter (with a Wireless icon). Right click on it and select Status. From the resulting window, click Wireless Properties button and click "Show Password" to see the password (under Security tab).
Is that the same password ***** were trying on your Kindle ?