32 GB of ram, only 16 is read by bios, windows and ubuntu

Hi everyone, I have an issue since some years that I have never succeeded to understand on what it depends I have a computer assembled by me with these features:
Processor: Intel i73770
Motherboard: asus P8z77-v deluxe
Ram: 32 GB, corsair CMz32GX3M4X1866C10
GPU: Gainward geforce 680
When I have assembled this pc for some months both windows and ubuntu they was reading 32 GB of ram fully. After some months suddenly it reads 16 GB of ram, from bios also if the rams are 1866 mhz I can take them only maximum to 1600 mhz. I can't understand why I have this issue and how to solve it. I attach to this conversation some screen of cpuz and windows properties.
Thank you for helping

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Windows 7 Home Premium is limited to 16GB but those screenshots look like 8 or 10 which can handle 128GB.

If you take a stick out then does the amount stay the same, drop to 12GB or drop to 8GB? Is the answer different if you take sticks out of different slots?
 
Thank you for your reply , I have windows 10 pro 64 bit and I haven't enabled memory max :
kZU44P.png

Yes I have tried using different slots and you know what it happens? if remove all, and put two 8 GB rams in same colour slots (so blue slots or black slots) computer detects 16 GB, if I put 1 8GB ram in black slot and 1 in blue slot, computer detects 8GB but SPD so CPU-z always detect all ram inserted
 
if remove all, and put two 8 GB rams in same colour slots (so blue slots or black slots) computer detects 16 GB, if I put 1 8GB ram in black slot and 1 in blue slot, computer detects 8GB but SPD so CPU-z always detect all ram inserted

With two sticks we can't tell is the 8GB is only one stick being detected or only using half the capacity from both sticks which is why I suggested three.

Does the BIOS show which slots are filled or just the total capacity?
 
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