I was devastated earlier today when I started getting an error on my Xbox 360 Slim saying I had a problem with my wireless network Adapter – specifically that I had to connect one when the Xbox 360 Slim already has the adapter built-in.
After much googling, it turns out that actually there is no hardware problem with the wireless network adapter at all but in fact some weird glitch involving the TV. So, if you’re seeing the same message do not despair!
All you need to do is turn off the Xbox and your TV. Next, turn the Xbox back on, wait a few seconds and then turn the TV back on. Weird but it works! This video I found should also help.