Installed Memory (RAM): 8GB (4GB Useable)

I have 4X 2GB RAM sticks installed, Windows 7 Ultimate x64 shows "Installed Memory (RAM): 8GB (4GB Useable)" in the system information. The motherboard says it supports up to 16GB of memory. I had Windows XP x64 and I'm pretty sure it was able to use all 8Gigs of memory. I've just formatted and am not burning through 4GB for sure.

*The BIOS only show 4096MB while booting.
I was only able to find one option relating to memory mapping and it took it from 4Gigs to 3 and change.
CPU-Z shows all 4 sticks as 2048MB
I went in to msconfig and checked the limits, they are not set.
I tried resetting the CPU and RAM sticks 3 times, the CPU has no pins to be bent (flat contacts, I5)
I rearranged all the RAM.
I have separate video memory from the system memory.
I have a 64 bit OS (I am 100% certain)

Hardware:
Memory: Four Corsair XMS3 TW3X4G1333C9AG
Motherboard: Asus P7P55D Pro
CPU: Intel Core i5-760 BX80605I5760
Graphics: Two ZOTAC ZT-50401-10L GeForce GTX 550 Ti

If anyone has new ideas or knows the exact setting in the bios, it would be greatly appreciated.