I've got an older Biostar motherboard T5XE CFX SLI motherboard where when I put in two 4gig DDR3 sticks, it only shows 3gig available under 64bit windows 10 and 64bit windows 7. I'm assuming there must be something in the BIOS causing this, possibly something I set in error in the past or to get the install to work. (i've just been using it as is for awhile and wasn't sure if I wanted to reset the entire thing in case it wouldn't boot happily afterwards for some reason, I thought it was just the problem causing W10 install i've had for awhile but when I re-put W7 back on in frustration it was still only 3gigs usable so realized it must be something lower level happening)
are u running the latest bios update...mite be a issue with your mobo that dont read more 3gig of ram. also have u tried resetting the BIOS to default.
i agree if u have 4 mem slots and is in this order blue orange blue orange the modules are inserted in the two blue slots or the two orange slots or what ever color your mobo has them.