How do I get the Marathon Man achievement in Halo 3?

[Neilio]

OK, so I've gone through and did The Ark, I red ALL THE WAY THROUGH the three terminals on that level, I mean I actually sat there and read them until it didn't go any further, even after the screen turns red. I waited until the little arrow turned red. Then I finished the level after getting all three of them. The I did the EXACT same thing for The Covenant and Halo AND NO ACHIEVEMENT!!!! I did all of them on normal AND in cronological order.
I also did it with scoring and 2 skulls on.

 

[tanner s]

Go to youtube and look it up. Make sure that you dont have any cheats on when you do it either because this can disable achievments.