Is this a used router you bought and never used before?
Is this a used router you've used before and just started going bonkers?
Have you tried setting different terminal speeds, in case someone messed with the config register -- 115k is popular for practicing xmodem ios image uploads. And for some reason, 36.4k is popular, probably because of modems, though I'm not sure why someone would put one on the console port when the aux port is right there. And try all the other random speeds until you run out of options or find a speed that works.