Hit the green button and enter the small platform to elevate you where you first were, overlooking the crates again. Now plant yourself along the dotted line so you can hop onto the moving crate. Allow it to take you into the compartment in the wall but remember to crouch when you get close. This uncovers another Quad Damage secret.
Exit the crevice and jump up onto the crates on the other side of the room in order to activate the yellow-coded door underneath you. Enter in the warehouse space and blast everything in sight. Be forewarned - when you go for the Chaingun, a box will blast open with a Beserker or two out for blood. Hop on the platform and snatch the first power cube. This will de-activate the red laser grid so you can walk past on the walkway above.
