1024kb: With drives ranging from 900GB SSD to 300GB SATA, you have hardware from across the ages. If your PSU is original and/or the same age as the 300GB SATA then it’s highly likely to be causing your problem. PSU’s at that age weren’t expecting RX580 cards & 4 hard drives. Well, maybe the 4 HDD.

It looks like you’ve had a long-term upgrade policy with this PC, you’ve probably added more/bigger HDD, the video card & more RAM over time. At this age, you’ve had your money’s worth from the PSU, it’s time to upgrade that component now.

with something that old, it could be any one of the 5 billion transistors in the box. i would agree that it's time to get a new rig, or start looking at getting a new rig.