Infinite key loop "BC"

[maxfubar20]

Recently my desktop has a strange problem. Suddenly it starts inputting keys "BC" repeating non stop. The only way to stop it is to restart. I swapped keyboards, ports, to no avail. It even triggers this problem when no keyboard is plugged in. I ran chkdsk, sfc scannow, even did reinstalling Windows (keep files). Nothing has helped. Any ideas?

Asrock z170
i7-6700k
16GB ddr4 3200

 

[maxfubar20]

For the sake of anyone else with this, i got it solved. Logitech g600 mouse malfunction. G7 key defaults to shift+B, in another mode, same key defaults to shift+C. Not sure what caused the initial problem, but unplugging the mouse stops the key entries.