Have you tried using a different Keyboard and Mouse?
Sounds like something took out the USB. I'd guess some type of rogue filter of HID's from an anti-cheat program. You're going to need to get into safe mode, but if it's a filter it'll still be there. Power the system up until you see the circles spin, then hold the power button until it turns off. Do this repeatedly until it says "Please Wait" then let it run. Do See Advanced Repair Options - Troubleshoot - Advance Options - Startup Settings. We want to go into safe mode and see if it works there. If not, does your motherboard have PS/2?
Can you get a PS/2 keyboard? That should work. Do:
Need to see what you have there. We're looking for lower filters, or an upper filter that isn't kbdclass. You might also do:
See if there's anything throwing an error in there. That'll give us information as well.
Yes, that'll work.
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