As with most Xbox Live users - I've had my fair share of troubles with this. Recently, I lowered my Virgin cable broadband from 20mb to 10mb, not that this should have a reason for Xbox live to fail?
I'm using one of the older cream Xbox 360s with a wireless adaptor with Belkin wireless N router. Since Saturday 2nd July Xbox Live has signed in once, randomly on Monday 4th July. I've rebooted the router, re-set the wireless adaptor, disconnected, re-connected - still no Xbox Live.
The connection test is successful to the router, then the internet then NO Xbox Live. Can anyone help? My gamer tag is "Rory Skywalker" - thanks for any help guys!