Hello, and sorry for the long post.
I decided to upgrade my motherboard and processor after 4 years, and after installing the Aorus x470 and R7 2700x, I couldn't get more than 3 USB 2.0 devices to work at the same time. After hours of frustration and phone calls to Gigabyte, AMD, and Microsoft support, the best advice was to reinstall Windows 10 Home and Pro, multiple times. Still, the problem persisted.
Concluding that the new hardware was malfunctioning, I decided to change back to my old hardware (Gigabyte GA-B150M and I5 6500), and reinstalled my copy of Windows 10 Pro. Note that this is the hardware and OS that I was running before, and never ran into this problem, even after using 4 USB 3.0 devices and 6 USB 2.0 devices. I also never updated my copy of Windows in the past, so I was probably running on a 17xx version, not 1803 or 1809. After reinstalling my old hardware, the problem persisted. I still cannot get more than 3 USB 2.0 devices working at the same time, which is frustrating and detrimental to my work.
I have tried all sorts of driver updates, BIOS updates and flashing, Windows power options, registry editing, etc, etc. I have not been able to find a solution. My problem seems to be fairly unique, as googling has not been super helpful. I am not sure how I still have this problem, even though the hardware is the same as I had 2 days ago. The only difference is the Windows version, and the associated drivers.
Is anyone else having the problem, and found a fix? Is it a problem with Windows, or something else?
The devices I am trying to connect are:
Flash Drives / External HDD
Any combination of 3 work, more than 3 causes static in the headphones, on/off cycling, etc.