please help will not let me get in the loby to join game

i have just recently purchased halo reach but wen i chose the network it will not give me the option to join xbox live party (it is blacked out) i can only join off xbox live friends or my console or a lan hook up…IT WILL NOT LET ME JOIN MAIN LOBBY

also in the menu screen my NAT is OPEN but everything else is undetected

I have been on the phone with Xbox live customer support 3 times trying to resolve this with no luck… so I am asking for a little help
Thanks

i have a 360S with a new 320gb HD

The ‘Xbox LIVE Party’ option is for those who are in an Xbox LIVE Party via the Guide, it allows you to see what others are doing in-game on the Halo: Reach Active Roster.

Im just trying to figure out how to join a multi player …i have no problems doing this in all other games like MW3 …
do they have to be on my friends list or can i join a random game??

You need to choose ‘Matchmaking’ from the main menu and then select the playlist you want to play from that list.

thank you very much