Problem with Gigabyte 970A-DS3P

Such garbage, a lot of applications are always running on the computer, so I recently decided to change the percentage - I took the FX-8350, respectively, I had to take a new motherboard, a video card and RAM (two strips of 4GB 1333mhz each) left the old ones - there were never any problems with them ..

Two weeks have passed since the purchase, everything worked like clockwork, no problems, but an hour ago I noticed that everything began to slow down a little, the dispatcher showed 15% of the processor load and 75% of the RAM ...



Too much, I decided and began to dig further, noticed that in the speed tab it says that I have 4GB of memory.
I went into the properties of the computer - 8GB, 3.96GB available

There was an idea that the problem was in the BIOS, so I rebooted the computer and rummaged around there - everything is normal, without changing anything I loaded Windows and now I have 8GB again, nothing slows down and everything is used.



Question - what the hell was it and what to do?

The warranty on the motherboard is alive, they will accept it without question, but today is Sunday and I’m too lazy to disassemble everything again (I bought a cooler for a percentage, not very expensive but the cooling is excellent and screwing it back is a whole adventure - a bandura of considerable size)