I've had my Xbox 360 Slim since last summer (so for about a year now) and I've never had a problem connecting, and staying connected, to Xbox Live. I usually use ethernet because wireless isn't very fast at my house.
Last night we had about 5 people over, all of which brought their own consoles and connected to xbox live. Now at first I thought that our internet had just been maxed out, as I couldn't connect last night either, but no big deal. I just hopped on one of their consoles.
This morning the problem continued, however, even after they have all left. My Slim connects to XBL just fine, I can play for a bit (about 10-15 min) and then I get disconnected. I've tried using another ethernet cord, same results, and I know the router isn't the problem (same router I've always been using). Then I tried connecting using the built in wireless that comes with all Slim models and I get the dialogue box that says, "To connect to a wireless network, make sure you have an Xbox 360 Wireless Adapter plugged in."
Well that's helpful...
So I've restarted the modem, router, and xbox, and the problem persists...
Any help you have would be awesome. I know all signs are pointing to my xbox being the problem but I don't want to hear that right away. Keep in mind, I'm not very tech savvy, so any keep help you can offer should be as dumbed down as possible.