Fixed Windows 10 problem of not detecting any keyboard and mouse at login screen

Yesterday morning, when I booted up my desktop computer running Windows 10, I was stuck at the login screen because the keyboard and mouse are totally not functioning. It had taken me more than 2 hours to fix the problem.

The symptom:

• The keyboard is not detected by Windows and not functioning. Pressing the Num Lock and Caps Lock will not toggle the LED light on the keyboard.
• There is also no mouse cursor on the login screen.
• The keyboard and mouse are functioning well if reboot into BIOS screen. This indicated that the problem is not with the keyboard or mouse or USB port, but something is wrong with the Windows system.

I have tried the following methods, but all of them failed to resolve the problem:

• Change to connect to different USB port of the computer produced the same result.
• Change to use another keyboard/mouse is also the same.
• When using a wired mouse, the LED light on the mouse is illuminated, indicating the mouse is getting current from the USB port of the computer without problem.
• Press the power button to shutdown Windows, and then start it up again, did not help at all.
• Boot up with Windows 10 USB Recovery Drive, the keyboard and mouse were working fine. Perform a Start-up Repair did not find any problem.

How I finally fixed the problem?

I unplugged the computer power cord from my UPS and plug it directly to the wall socket. Then, switched on the computer.

When the computer reached the Windows login screen, cut off the electricity supply by switching off the wall socket.

On the next reboot after Windows encountered such an "unexpected power off", my keyboard and mouse are finally functioning again.

I know that this action of forcing unexpected power off was quite harmful to the computer hardware as well as to the Windows system, but it somehow managed to trigger an automatic repair during Windows startup which fixed the keyboard and mouse issue.

When everything was back to normal, I connected back the power supply of the computer to my UPS and tried to find out the cause of the issue. It was caused by an unsuccessful automatic update of "Cumulative Update Preview for .NET Framework 3.5 and 4.8 for Windows 10 Version 2004 for x64 (KB4570721)". 

The update was then done manually after some precautions taken. It was successful and required a reboot. Luckily, after the reboot, my keyboard and mouse are still functioning well.