Some users have reported that their ADB keyboard are sometimes 'dead' (though
the mouse works fine) when they start up a Macintosh II or SE. One reported
cure has been simply to unplug the keyboard then plug it back in.
Caution: this fix works only if the mouse is plugged into the second ADB plug
on the back of the computer. If the mouse is plugged into the keyboard, the
fix (unplugging the keyboard then plugging it in again) crashes the system.