can't add ram in black slot

[aspri]

hello fellas,

first of specs:
asus p8z68 m pro
i5 2500k
2x4 hyper x savage ram
gtx 770

ok, i had a x2 crucial ram sticks aside. I wanted to add more ram, even if the brands and speeds had nothing in common.

I started by putting ram in all 4 slots. There's a MemOk led on the mobo. Turns red, doesn't goes past the test.
the Hyper ram in blue slots and crucial in black.

I thought it wasnt working because I couldn't mix up the ram. But I was wrong.
Took the hyper ram. Tried the boot the pc, memok led still on.

I thought it was the crucial ram that was faulty. Took it away blablablabla, finally tried it in the blue slot, pc booted and it was ok.

I then suspected the black slots. Put one of Hyper and one of crucial in the blue slots. Everything working, CPU-Z shows the 2 sticks and reports 8 GB ram.

So, the big problem are the black slots. Any idea?

 

[aspri]

ooooops, couldn't put the same ram in dual channel, so I put

Hyper/Hyper/Crucial/Crucial
Blue/Black/Blue/Black

rather than

Hyper/Crucial/H/C
Blue/Black/Blue/Black

And it's working