Instructions
Check to make sure the power is on for the source of your wireless Internet, whether it's a router or some other source. Make sure the router is actually broadcasting a signal by checking it on a home computer.
Make sure an Ethernet cable is not already connected to your Xbox 360. Look for any devices that may be directly interfering with the signal from the source to the console. Remove any object in the path of the signal to the console.
Make sure your console's MAC address is listed if your Internet is enabled for MAC filtering. Look in the Advanced Settings menu on the console to find the MAC address. Log in to your router by opening a new browser and going to the "192.168.1.1" address. Click on the "Wireless" tab and select "Edit MAC List." Check the list for the Xbox MAC address and add it with the "Update" function to set up your console's connection.