Is it possible you had assigned a static IP to the OBi that is now either in use by another device or is outside the subnet of your new router?
Or maybe it's just a matter of pulling the power on the OBi, wait 20 seconds, plug power back in. If you haven't power cycled the OBi, it's trying to communicate with the DHCP server on your old router and not getting an answer
(Over simplified, but makes my point.)