Gigabyte UD6 Memory Problem

Hello.
i buy 4x4BG G.Skill Memory 1600MHZ and try to put in slot 1,3,4,6 and get "C1" Error.
i try only 4x2 put to slot 1,4 my computer i up but i see only 4 GB in Bios and in windows i see 8GB (3.99 Gb Unsable)
Try Up Voltage For memory to v1.65 And nothing...

Processor : i7-875k Unlocked.
Motherbord : Gigabyte P55a-UD6
Memory : 4x4GB G.skill
Graphic : Nvidia 780 Ti
Power Supply : Seasonic 750W 80+ Gold X
cooling : Corsair Hydro H110
Sound blaster : Creative ZXR

OS : Windows 7 64x Ultimate
Bios version : F11

Any idea How Fix it?
Thanks for help

It might be possible that you might have a faulty RAM slot, you will be able to use dual channel in p55. You can try to test if its faulty slot or module is to just put one stick in the slot and start with slot number 1 and go through each slot. Incase it is working then it will boot nto Windows from any slot with just one stick. Also are you using 32bit OS or 64bit OS?