Try shutting down your console and then unplug it for 5 minutes. After 5 minutes then plug it back in and try connecting to the wifi. If that doesn't help the wifi hardware may have died.
The built-in wi-fi on XBOX360 models that have that feature does uses only the 2.4ghz spectrum. I have read reports that the black XBOX 360 N adaptor does support 5ghz but I find that quite dubious since mine clearly does not and I found no product literature that says otherwise when I searched.
Connect you Xbox 360 to your network. Both wired and wireless connections are available to all … Amazon.com: wireless adapter for xbox 360 G-Dreamer Xbox 360 Wifi Wireless Network Adapter A/B/G & N Networking Adapter with Dual Antenna for Microsoft Xbox 360. by GDreamer. 3.7 out of 5 stars 5. $49.95 $ 49. 95. FREE Shipping. Only 7 left in stock - order soon.
Jun 29, 2018
Why can't I connect to Xbox live or anything via wifi? Answered: Do I need a wireless network adapter in order to connect to WiFi on the old Xbox 360? Unanswered: We can use wifi connection in xbox 360 4gb kinect bundle without buying a wifi adapter or not? Answered: We can use wifi connection in xbox 360 4gb kinect without buying a wifi How to Connect Xbox 360 to Windows PC - Online Tech Tips Oct 21, 2010 How to connect an Xbox 360 - Shaw Support