Well, this morning nothing appeared even if I did reboot, multiple times. I checked the monitor, but that was OK, so it must have been either the video card or the motherboard.
Hmm. I kinda hoped it wasn't the motherboard, because replacements never work with older hardware (as in, anything not made the previous week). So, I went out and bought a GeForce 9800; I could have gone for something more flashy, but my hardware isn't up to it and I don't run Vista so it would have been a waste of money (like, indeed, Vista itself). I was a bit annoyed at having to do this, in part because the GeForce 9600 GT it's replacing is less than a year old, but also because I was cultivating a strange, crystalline dust structure on the fan output which was destroyed in the removal of the side panel:
Yeah, I know you can't see it very well from the photo but it looked like some kind of 3D snowflake alien blister infection.
The new video card needed two power supplies, rather than just one. Well, the old one was supposed to have two as well, but it worked with one so I didn't attach another (and no, attaching another didn't revivify it). The reason I ran it on one was because I only had one spare. Time was, the inside of a PC was packed with 4-pin power supplies; this one only has three, including the one for the video card. So, I disconnected my second DVD drive (which I'm not sure why I have anyway) and hooked that up. Well, I would have hooked it up if the cable had been long enough. It wasn't, so I had to put the new card in a different slot in order to reach it. There, it worked. Worryingly, it also worked when I took back one of the power supplies.
Hmm, maybe if I'd put by 9600 GT in that slot it would have worked, and I'd have saved myself a hundred quid?
Nah, that's crazy talk!