Why does my xbox360 says un-join able

I have xbox 360 Halo 4 and now I have xbox-live gold. When I try to play it says un-joinable and will just stay with no way to get online can some one point me in the right direction please. I have no friends on xbox live, and I just would like to play it online to see what everyone says about it. Thank you
HARRY

Hey if you’re still having problems this may help you!

Have you changed your settings to that you are playing on “xbox live” not “local” ? It got me the first time I went onto Halo :stuck_out_tongue: