wifi has the self-assigned ip address 169.254.94.108

I connect via a router to the outside world. I have two MacBook Pros, mid 2009, so am asking this rom the one that connects, via the same router!

Foe no obvious reason, after closing the lid last night on a machine that connects and opening it this morning, the Wifi icon at the top of the screen has a cute little exclamation mark in it and I get the following in Network Preferences:

I have read several apparent solutions, and attempted https://www.igeeksblog.com/internet-not-workidiscussng-due-to-self-assigned-ip-address-on-mac/ but had no success.

The machine will connect to a neighbour's network and communicate away happily via their WiFi. Yes, I had their permission! That is how I got the screenshot onto this machine and could post it.

I then deleted the wireless network in the box above and attempted to reconnect. It asked me for the password, and then came up with the same message.

I'd appreciate any help folk here have to offer me, please. I don't need the machine online much more, I have a replacement machine on order, but I to want to ensure I can run it for its last few days!