My brother has been having some trouble with his xbox live for the last month or so, when he is online he can still be invited to games and have private chats and basically utilize all the functions of xbox live... accept no-one can actually see he is online. Effectively it is the same as being set to appear offline but it is automatically like that and he can't do anything about he even though his profile is set to show him as online. I don't know if anyone else has had this problem and knows how to fix it, he has a gold membership. Hopefully someone here on GB can help.

Hmm. Sounds weird. First thing that comes to mind are the NAT settings. Everything alright there? Like open?
Apart from that, has it always been that way, or did he maybe change anything?
Also, are you your brother??? :P