You've got an apipa on the Ethernet connection and a class b subnet, I take it you're using the wireless to connect from the windows machine to the network, it shouldn't make a difference but have you tried disabling the Ethernet adapter?

Nope, the wireless connection goes to the Internet.

The NAS is connected via Ethernet to the same switch as the Windows machine. (The NAS doesn't connect to wifi.)

Can you restore from backup to when it was working?

Only if you can supply me with a time machine so I can go back and create a restore point...

Turned off system restore?

Definitely don't have access to another windows system just to try?

Pretty sure Ant can build you one with a rasberry pi.

Nope, but there's only one restore point - created automatically on Friday evening - so that doesn't help. (Ticked the "Show more" checkbox and nothing else appears. Damned thing.)

I have no other active Windows boxes, and I'm not faffing around finding and swapping the harddrive I took out of my netbook since I'm approximately 5000% certain the NAS is correctly configured and the issue is with this Windows instance.

Does the network interface use DHCP or a static address? Either way, you shouldn't be getting a 169.254 address on the interface, so either check that DHCP is still working, or assign a new address to the interface.

No DHCP server, afaik. I did originally intend to setup DHCP+DNS on my Pi but didn't have time initially and then everything was working with 169.254 so I just left it.

Do you still not have a phone line?

Aye, s'what I was thinking.

Can you connect to anything else on the Ethernet adapter? Config looks a bit... nonstandard.

Don't be shocked.

The network engineer in me thinks that 169.254 should never be used so that it's obvious when they crop up that something is wrong. But then there's at least one example of paid work that I've done which uses them for the wireless access points VLAN. Such a cowboy.

Give it a proper IP address and see if that helps.

Definitely some totally unconventional setup going on here, which is no surprise.

I can SSH to the Pi via it - at present only the three devices are connected.

Hey, I'm still celebrating finally having a device that does 4G. :C

Yep, gonna have a go at setting up the Pi as a DHCP server, but probably tomorrow when I'm (hopefully) less tired.

There's nothing deliberately unconventional - it really was just get the NAS connected enough to shunt files around and make space on the main machine and I'll set things up properly later, then it's always just been oh it's working good enough for now.

I fecking hate "good enough for now". :@