Chris,
With the A400, you need to connect your PC to the console port of the A400 using the serial cable (BTW, you could have purchased this cable in any computer store). Follow the information in the user guide for installation in chapter 3 (use hyperterminal set to 38400, None, 8, 1, no flow control). Power the unit off, power back on and when you see the prompt to “hit enter within 3 seconds to change any options” hit enter. Go through the boot up menus and the last option will be to restore to factory default, you must say Y to this. This will wipe out your entire configuration, including the password, but not your IP address information. This is the only way on the A400.
Mike