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#11
When your PC is turn off, but still connected to power outlet, it has a "Standby power supply" running at all time (+5V)!
All desktop PC work like that! As long as there is power to your PC's Power Supply, but you have shot down Windows, then
this standby power supply (+5V) have to be there, so that your PC are able to turn ON again, when you need it!
This standby power supply (+5V) - supply 5V to all USB connectors, unless set to not do that, in Windows Power setting!
Allso this +5V will run a standby LED light, normally @ your PC power button, to tell you that it's ready to turn ON!
If you want all power to be OFF to your PC (= No standby power) then you have to switch off your Power outlet (Wall plug).
I am just explaining how all desktop power supply's work. There will always be a standby power (+5V) and a LED light ON,
unless you turn OFF the power to the power supply!
Good news, guys. I fixed it! All I had to do was reset the CMOS data using the onboard jumper. Then, I set up the BIOS for the most crucial things (e.g. setting SATA mode to AHCI, disabling unnecessary onboard devices, or setting the proper boot device). Now, when I shut down my PC, none of my USB devices work afterward. I guess I must've messed up some BIOS settings. I was also pointing out the wrong suspects. Nevertheless, I want to thank you all for your concern and help. Even though your pieces of advice didn't help me with my problem, I did learn valuable things. Thanks again. Problem SOLVED!
Quick edit: Alongside the reset CMOS, I still need to have the Fast Startup disabled (I re-enabled it after I thought I'd succeeded, the problem reoccurred). Fortunately, the difference is little to none, so I don't mind it being off.
Ok, thanks. Will remember that too.