When you say the power was cut to your USB keyboard, could it perhaps have been reset and in a unenumerated state? If you have a multimeter it could be useful t

When you say the power was cut to your USB keyboard, could it perhaps have been reset and in a unenumerated state? If you have a multimeter it could be useful to check the various power rails in the bad state. Try running Memtest86 and lower the temp while it runs.