Halo 3 skulls? im confused.?

[cok.anut]

When i play on halo 3 and got to where the skulls are on normal difficulty, there not there i have completed the game before but never collected the skulls, i didnt start the level from the begining, i dont know if they might be reasons. Do i need to turn any settings on? Any help please.

 

[perfecsaiyan]

To get skulls:

- START from the BEGINNING of the level
- Play on normal
- Some skulls will disappear if you trigger a checkpoint before grabbing the skull.