Could be PSU (Power Supply Unit) is bad? You didn't mention that.
A PSU's voltage control eventually messes up or you've added too many peripherals draining your PSU.
I had something similar happen. Weird errors, problems... It was a mystery.
One time, replaced PSU and all problems went away. It was a cheap PSU that came with the case.
Another time, I loaded the PSU with too much peripherals, nothing worked right.