AX1800 - Not connecting

[Buelle99]

We successfully connected the extender to our modem and all worked fine for 9 days.  Today, it stopped working and said it can't find router. We reset and repeated the set up and still not working.  Any suggestions

[CrimpOn]

 The first step is usually to identify the make/model of the ISP device and the Netgear device.  AX1800 is a marketing term describing some fantastical ideal of bandwidth (which bears no relation to reality). The actual model number will be on the product label on the bottom of the device.

It appears that the terms "modem" and "router" refer to the same device?

(The devil is in the details, or so I have read.)

[plemans]

Did you set it up using the push button WPS option? 
If so, factory reset the extender  and set it up using the installation assistant.
To factory reset, push and hold the reset button for 7-15 seconds while powered on. 
Here's a video of how to use the assistant. 
https://www.youtube.com/watch?v=yJVklshxBMk