halo 3 problem please help?

[Wesley V]

on halo3 they achivments for finding the skulls on either normal heroic or ledgendary. when i pick the skulls up i dont get the achivments im doing it on heroic am i doing smothing wrong? and does anybody know why im not getting the achivments
i am picking em up and i checked i didnt get the achivment

 

[=) yasmin!]

You get it if you pick it up. Silver skulls don't give you that in-game "Achievement Unlocked" massage like other achievements do, but you still get credit.

 

[Jake W]

are you picking them up hehe