Also try the emergency interrupt polling code. If the usb keyboard
works with the emergency poller but doesn't work otherwise then we
will know that it is an interrupt related issue. If that turns out
to be the only solution then you would also probably have to increase
the polling frequency from 10 to 100 (it is 10 by default because we
want people to notice that interrupts are broken instead of just always
relying on the emergency interrupt polling thread).
In /boot/loaderconf:
kern.emergency_intr_enable=1
#kern.emergency_intr_freq=10
-Matt