Have 8gb RAM, motherboard only detects 4gb

[Jpok]

I really can't figure this one out. Here's the specs:
Mobo: GA-P55-UD6
CPU: core i7 860
RAM: 8gb Corsair Dominator, made specifically for socket 1156 architecture
Cooler: the famous Noctua one
OS: Win7 64-bit

The bios only detects 4gb, and Windows 7 64-bit only detects 4gb, but CPUZ detects 8gb installed.
I've gone through every bios setting, and I can't figure out why only 4 gb is detected. BTW, The RAM is installed in the correct slots according to the manual, slots 1,2,4, and 5.
Thanks for the help!

[Jpok]

Okay, I fixed it. Writing here to help others.
What I did: (sorry, it seems kinda random, maybe it was just that a module wasn't seated correctly, but truly there was no physical evidence of this)
I'm dealing with 4 x 2gb modles here.
Removed 2 modules, left 2 in the system. Bios reads only 2 gb. Something's wrong.
Swapped the 2 in the system for the 2 that I pulled out earlier. Now bios reads 4 gb. Getting better.
Added only a 3rd module. Bios reads 6gb
Pulled out that one, and swapped it with the other remaining module. Bios still reads 6 gb.
Put the 4th module in, and finally have 8 gb.