Hey there Maher13,
I'm sorry to hear that your Chromecast with Google TV is having issues with your Wi-Fi. These networking issues can be pretty tricky, so I'd be happy to help you out. First, go ahead and follow the steps listed in this article. If you get stuck on any particular step, or if you encounter any error messages, please let me know.
I look forward to your response, and if you have any other questions or concerns for me, I'd be happy to address them.