Windows 7 64 bit ram issue

I recently built a rendering desktop, I'am running windows 7 premium I was told that windows 7 premium will use a maximum of 16g of ram. I currently have 12gigs installed on the motherboard (matched trips), windows 7 premium only uses 8gigs out of 12.

I need windows 7 to use all of the 12 gigs of ram is this possible...below is a spec of what some of the hardware is

Motherboard: X58 FTW^3
GPU: NIVIDIA GTX 460
WESTERN DIGITAL CAVIER GREEN HD 4 @ 500G (RAID)

What BIOS version are you on? I think that you will need to upgrade your bios version of your motherboard. Another thing is, in MSConfig, under the Boot tab, if you click "Advanced options", "Maximum memory" should be unchecked - is that the case? I don't think it's a hardware problem as such if Windows can see there's 12GB, which apparently it does, but elects to use only 8GB.

Thanks for the info...