Trouble installing extender with new modem

Hi there,

I've been using the extender successfully until now. However I have a new modem/router and while I have been able to pair the extender to the new modem it does not show up on any devices and the red light is on showing no connection to devices. In my wifi lists on my pc and iphone the old connection to the old modem is showing but not the new one.

Any help would be much appreciated,

Thanks

Nikki