What is Going Wrong?

Windows 10 latest pro machine. Several weeks ago I was unable to boot into BIOS or anywhere else. Unplugged machine and after plugging back in, everything worked. Now, however, I am getting a message that USB device over current detected. I removed all USB devices, leaving only monitor and wired network connected. Still getting the message.

I looked at those, but none of it makes sense if I still get the message without having any USB devices connected. I think it is probably a PSU problem.

Steve C said:

Might be worth changing the CMOS battery then loading the BIOS defaults

I wonder how old the system is?

CMOS batteries are usually good for years.

Clearing the CMOS may be a good idea, all the same. Most motherboards can do that by shorting two pins, or pressing a button. It isn't necessary to remove the cell.

Steve C said:

I turn my desktop PC having a Gigabyte board off at the mains when not in use. In this situation the CMOS battery lasts no more than 2 years. The PC fails to boot once the battery voltage drops to 2.8V.

I do the same. But I'm not sure whether I have ever observed the life expectancy of a standard 2032 Lithium cell under those circumstances.

No reasons not to replace them, even absent a voltmeter. At least in the US, they are cheap and commonly available. (I've found them powering musical greeting cards.)

Have a look on the rear of your motherboard for connectors which share the same block as the USB. If you have a LAN connector plugged into the same shared port block as the USB, remove LAN plug and then do a reboot, to see if the problem persists.

Panasonic 2032 cells are very good and will last for a while.
Yet ive found cheap supermarket 2032 cells are rubbish.