Halo 2 problem???

Why can't i play halo 2 on xbo live on my 360? When i log in to my xbox live account it says that there is an important message from xbox live and asks me if  i want to go to account management, when i do there ain't no real message so why won't it let my play halo 2 on xobox live?

Well I'm 15 that ain't to young to play but i checkeed it out it was just that the original xbox games were blocked from being played online by my 360. Thx a lot