12 Gigs of Ram only 5 Gigs usable??

[phillywilly]

I run Tri Channel 1600 Corsair Dominator, 6x 2GB RAM. I've been running 6 gigs and had no issues, and all the memory was read, now after I installed the 12 , System Properties in my computer says only 4.99 GB usable out of the 12GB. Please help. DXDIAG also reads the 12. Task Manager only shows 5.111 gigs. :/ Im sort of new to BIOS features and all, but I think I can find my way.

 

[phillywilly]

i am also running win 7 64 bit ultimate