RAM slot problem.

I bought today 2 strips of Kingston KVR13N9S8 / 4 4gb RAM (there used to be 1 spectek strip for 4) When I installed all the strips, it turned out that the computer sees only 4gb instead of 8. In 20 minutes of rearranging the strips back and forth, I found out that only one slot works. If you turn on the computer with any bar only in the first slot, 3 short bios signals are heard at startup (if you start with a bar in the second slot, everything works fine). Plus I checked the slots of the RAM with the Speccy program, even with the strips inserted into both slots, the program shows that one of the 2 slots is free. Motherboard A960M-M3.