Need help connecting to XBL

I got a wireless receiver that hooks into my xbox for my birthday in april, and my dad switched our internet provider to comcast a couple months later because "it wasnt fast enough", they gave us some crappy wired modem, ive tried hooking my xbox directly to this modem but when ever i test the connection it doesnt even show that internet is available, how the hell can i fix this because ive found nothing helpful on microsoft or xbox.com (like they ever help). What should i do? (thanks for any input)

Have you tried reading this? 
http://support.xbox.com/support/en/us/nxe/xboxlive/getconnected/hcxl/getstarted.aspx   
 
It has lots of info on how to connect your 360 to different setups.