That ADSL modem router WiFi firewall box thingy that apparently wouldn't work anymore?
It does work.
It did come up on its default address of 192.168.1.1, but there was a reason I'd failed to be able to connect to it. Now, I'm perfectly aware that a /24 netmask on my PC would prevent my machine on 192.168.0.5 being able to see it, so I'd widened the netmask to a /16.
What I'd forgotten, at 01:00, is that the router would then receive the packets, but be unable to return them, because its netmask was still a /24.
Last night, I switched my IP address to 192.168.1.5, and suddenly the router was there after all. In a totally virgin state, admittedly, but that's why I have a backup of its configuration. Uploaded that, let it restart, reverted my IP address, and it was all hunky dorey again.
Oh well, it's nice to know that we have a spare working router if it does decide to die (and £25 is not a lot of money for that peace of mind). And that I know where all the password and logon details are.
In other news, the graphics card, the one that wants a minimum 450W PSU and that had been somewhat flaky when run with a 430W PSU, didn't get any more reliable when hooked up to a 700W PSU. So we also have a spare PSU for next time one dies.