a: on that router, I believe it is DHCP on the WAN interface (ether1), and 192.168.88.1/24 on the LAN interface (ether2). You can look it up on the box it shipped in, or reset in hardware as described in b) and then access via serial console and look at IP configuration.
b: "/system reset-configuration" if you can access it (IP, MAC, or serial console), or follow the instructions for a software reset by shorting the reset hole as described in the device's hardware manual (http://routerboard.com/pricelist/download_file.php?file_id=143
c: if you're unsure it's always best to use the serial console.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.