Z77 Extreme4-M - Memory Issue

Hi all,
Hi have this configuration since 2012, and it has always worked well and it was very very stable :

- ASRock 1155 Z77 Extreme4-M
- CORSAIR DDR3 16Gb (4X4GB) 2133MHz CL11 Vengeance Red (CMZ16GX3M4X2133C11R)
- VGA GTX 1060 6GB (installed on 2018)
- Intel 1155 i7-2700k Ci7 Box (3,5GHz)
- LC POWER 650W OZEANOS 140MM PFC 80PLUS V2.3 (LC8650II)
- Dissipatore NH-U12S (installed on 2016)

Yesterday I found the PC in a strange state : video signal off, keyboard and mouse off but led and fan on. I forced the reboot, and in Windows I noticed that only 8gb has been recognized by the system (16gb installed).

In the bios I see this:



But in the system browser a I see all 4 memory modules :



So i did some tests :

If I install 2 modules in slot1 and slot3 : Ok (8gb recognized)
If I install 2 modules in slot2 and slot4 : Ok (8gb recognized)

I did some memory test with this configurations:

Module1 and Module2 on Slot1 and Slot3 : OK (2h memory test)
Module1 and Module2 on Slot2 and Slot4 : OK (2h memory test)
Module3 and Module4 on Slot1 and Slot3 : OK (2h memory test)
Module3 and Module4 on Slot1 and Slot3 : OK (2h memory test)

Instead if I test all the 4 module together, only 8Gb were recognized and I get many memory errors:



I also tried this :
- Clear CMOS (5 times)
- Remove CMOS battery
- Remove all SATA device
- Remove all USB device

But nothig changed.

I also tried to remove the VGA Card, but I can't see anything from the onboard card (no video signal) : it disappeared.



Could someone help me understand the problem ?