How come I can't play Solo - Multi / Xbox Live in Halo 3?

When ever I try to play like Team Slayer or Something in that category i will be sent back to the waiting lobby ( I will get into a match with people and then get sent back to lobby which is giving me Exp Penalties.. ) Anyways I'm not sure if it's because my Brother moved my 360 while it had Halo 3 inside it and something happened or its Halo 3 I don't know .. ( O and I can log in to Xbox Live and chat to people but cannot play Matchmaking Forge Campaign or Solo Mode.. ) So can someone help me please.. Thank you

How come I can't play Solo - Multi / Xbox Live in Halo 3?
I know the entire Xbox Live network has been having troubles this past month. So it's possible it could be related to that, but it also might be a problem with your router. On the dashboard go and do an Xbox Live connection test and if it says your NAT type is strict than that could be the problem. If nothing about your home network has changed and the problem is recent it might just be a problem with the Xbox Live network at the moment. I hear they're working to fix it and we all get a free Xbox Live Arcade game soon because of the problems they've been having.