Ok, another thing, very insignificant, but sometimes helps....
Are the RAM sticks slots placed in the same slots that they were in, I know this is a highly illogical question and as if it makes a difference, but, believe me, windows rigs are sometimes very finicky and the stupidest things seem to sometimes cause the worst of problems, in my experience, try shuffling the sticks around in their slots. one of the combinations will give you the full amount of usable RAM, if everything else is fine with the rig.
Also check for shared memory with the GPU..... if there are setting in the BIOS which lead to it.