asrock x370 gaming k4

Hello, i would like to have some help with my current problem. I have an Asrock x370 Gaming K4 Fatal1ty Motherboard, an amd Ryzen 1800X and 16 gb ram, 4x4. I was using this setup flawlessly until today, suddenly powered on my pc, and violá, the system only recognising 7,95 Gb of my 16 Gb...