Before you connect kindle fire to the internet you need to check the points mention below:
1. Internet is Working: You need to assure that internet is working properly and is in working state. You must check out speed of internet by connecting with other device for checking its working status.
2. Turning off airplane mode: In case you turn on airplane mode and you getting issues when connecting with internet then you must experience the old kindle won’t connect to wifi error. This is important to assure that airplane mode is turned Off.
Inputting Wrong Password: Mostly when you input the wrong id and password can occur. kindle fire won't connect to wifi You must assure that entering the id and password are completely right.
Going for Software Update: Many times not updating device software can cause many complicated issues so you need to regularly install the latest updates on your device.