Have you emailed the manufacturer on how to reset the machine? I would do that first cos the manufacturer knows best and they should modify their UI to reject invalid IPs too.

Look inside the machine. Is there a jumper or switch inside labeled reset? Or some sort of battery? I hope there is a reset switch somewhere inside.

This a tool to find IP from mac address:
http://www.youngzsoft.net/cc-get-mac-address/