Problem with RAM, BIOS shows 16GB RAM but Windows recognises only 8GB.

[mehmmedd]

Hello, everyone!
First of all, this is my system configuration:
Intel i7-6700k 4.00GHz
NVidia GeForce 1060 6GB
&A 8GB 2133MHz
ASUS H110M-CS

I'll explain my problem here in simplest way as I can (sorry for my bad english). My PC have J&A 8GB 2133MHz RAM, so I decided to buy the same memory to make my system 16GB RAM. My mobo have only 2 RAM slots. My old memory was sticked in A1, so i sticked the new one to B1. Everything is fine until, in BIOS its shows DRAM status: A1 - 8192 MB and in B1 - 8192 MB. but when I log in to Windows, the System shows that i only have only 8192 MB. I decided to download CPU-Z and the funny thing is that, CPU-Z also shows that I have 16GB just like BIOS. So i decided to switch ram sticks.
1 - Old ram stick to B1 - it didn't work
2 - New ram stick to A1- didn't work
3- It only works when i use the old RAM stick on A1( then it shows in bios 8192MB) or when I use the old one with the new one on B1(then shows 16GB).
I can add pictures from BIOS,System and CPU-Z if its necessary.
Help me guys!

 

[Calvin7]

Adding extra memory may require lowering the clock speed, relaxing timings, and/or increasing DRAM voltages to get an extra module to work together with old memory. In any event, they have never been tested together and carry no guarantee that they will work together or how they will work together.

 

[mehmmedd]

So what should I do? May increasing the DRAM voltages can be the solution of the problem, or is the problem in the new memory stick or slots?