I need help with Halo 3 skulls?

[garrey1000]

Ok i'm playing halo 3 and i know where the iron skull is....do i have to beat the game first on normal before i can do that or will it be there right away because it is not there and its really frustrating me. Please help
Thanks
so i have to start fromt he very begging of the level i can't skip parts???

 

[T Short]

you have to start the level from the very beginning it will be there, i had the issue when i was trying to get them.