My router has an identity crisis? IP is giving me neighbor's router, not my own.

My router thinks it's my neighbor's router, or something to that effect.

Background: I have a PC connected via 'ethernet' (with the over-the-mains adapters) as well as a Linux machine on WiFi.

Both computers tell me my default gateway is 192.168.1.254, and that's also what my Pace router's default IP is supposed to be. However, when I connect, I get an ATT page (I'm not using ATT) that says the network ID is 'banana' which is my neighbor's network. My password does not work on it, either.

If I turn my router off (disconnect power) I can't navigate around that page (the router page / settings) on either machine, which should rule out some weirdness with the over-the-mains adapters, I think. 99% sure I'm not connected to the neighbor's (PW protected) network.

If anyone has any clue about what might be going on, or what I could look at for more troubleshooting, I'd love to hear it. Everything is default about my setup, and the internet works fine. I just can't access my own router (this started as me trying to add a second access point).