Windows 10 not detecting all ram installed

Nov 4, 2018
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People I have two Hyperx Fury 8GB Ram memory, one of them 1600Mhz and another 1333Mhz DDR3.
When I install both Windows says that there is 12GB installed being 8GB usable.
I have already done the procedures recommended by Microsoft in msconfig, I did not find option of memory remap in my bios, I updated the bios to the newest version available in the manufacturer's website, I changed the memory of slot and nothing solved.
The only way to work normal was to use only one of the memories, then windows recognizes and uses the 8GB.

Ideas?

Motherboard Gigabyte GA-78MLT-S2 (REV. 1.1)
CPU AMD FX-6300

PS: I have another 4GB memory when using it along with one of the other 8GB windows recognizes 8GB and uses only 4GB.