Computers are very stubborn fellows. If something doesn’t work, it usually doesn’t make sense to try it again. However, since WiFi is as unreliable as humans are, you can try to impress the router with your determination by making several connection attempts. Especially if the signal is weak, this often works. If you were connected to the router in the past and Windows tried to automatically connect when you booted up, it can help to disconnect and then connect again. Click the WiFi symbol in the systray, select the WiFi router you are connected to, and click disconnect. Then try your luck again and connect.