Question Fortnite laging

[Luke45]

Can anyone provide me a reason why is my pc lagging in fortnite and most of the other games.
And just if you need my system specs
CPU: AMD athlon x4 860k
MBO: ASUS a58m-k
RAM: 1x8 gb 1600 mhz kingston
GPU: XFX RX 570 8GB (1 year old)
HDD: toshiba dt01aca100 1tb
PSU: LC Power 6550 550W (1 year old)
CHASSIS: Cooler Master K280
OS; windows 10 pro

 

[Luke45]

My pc was runnig fortnite at 80 fps just fine and now it started lagging, could it be that cpu is old 6 years or my 1x8 gb ram