Why I'm connected and the signal is strong and I can't use the I internet with my window 8?

You are connected to your Wi-Fi network but something has not been set properly to allow you to access the Internet. Turn off the router and the computer. Turn the router back on and the turn the computer on. This will establish a fresh connection and everything should be working as expected.

Is your Wi-Fi router connected to your broadband? Is it connected to the Internet?
What firewall are you using on your PC?