Why does Windows 8/8.1 not see the memory bar?

Question

Windows

Anamnesis:
No more than a year has passed since the assembly of the computer. During assembly, two 8GB DDR3 Viper RAM sticks were inserted, the OS saw and used both.
After a certain time and one departure, Windows stopped using one of the memory bars, and even saw it (16 GB is displayed in the computer properties, 8 in the Task Manager).
I poked the planks this way and that, I took the motherboard to the service, I updated the BIOS - nothing had any effect.

Answer 1

Try to check the bar on another computer, maybe it's covered

Answer 2

check "Maximum memory" setting, msconfig-boot-advanced options, same story I had on windows 7.