MR80 Mesh Router Not Responding

I really appreciate your interest in helping.  This is the first time I've chimed into a community thread.  We are genuinely hoping there is a fix to the problem rather than a replacement cost. Our satellite internet is routed from our ISP through their modem.  The correct modem model is UniFi GP-J240-030G. We plugged in our new mesh system 16 months ago. If the internet is slow throughout our home, which happens occasionally in our rural area with a family of 7, we power cycle the modem and reboot the router/satellites. This has been a successful quick fix.  This happens every three months or so.

Within the last few weeks though, one of the LAN wired satellites would not sync with the router and push WIFI to our devices. After following the procedures in the manual multiple times, including your procedure, attempts to restart, sync, reset to factory settings, and delete/reinstall app, still will not connect the router to the satellites.  Now the router does not connect to the internet or respond to the Nighthawk app. During the app "New System Setup" process, the final screen always displays, “router not found.” Consequently, the router will not allow us to login to it for a firmware update, which was the goal.

I directly connected to the MR80 mesh router by connecting a LAN line to it from my computer. No IP address or gateway IP address is provided from the MR80 when I do that.  And as mentioned, the Nighthawk app also can't connect to it. The internet works if we bypass the MR80 and wire directly into the ISP's modem.  What else can I provide you with?