wired connection to router not working after new router and ex3700 extender connected

I recently got a new router, after which I have tried to set up the the NETGEAR extender ( via wired connection) - initially without the factory reset and just via using the IP address on the extender. However when I do it affected my wired connections to the router ( burglar alarm, tv and home automation system. I have since then tried to reconnect via pressing the wps (on the router and extender) and then by the factory reset option, however this constantly affects my worded connections. And also constantly changes the extender IP address.