Bloody computer started restarting randomly again. Same behaviour as before. At the suggestion of a few people, I checked my RAM. I did a memory test, took out my RAM modules one by one, checked each one, swapped sockets, etc. Near as I can figure, one of my RAM sticks is bad. It failed nearly all the tests on every pass. The other one had no errors on every pass. My computer friend agrees.
I’m operating on a mere 512 MB, until I get a new stick. It’s not so bad. At least I can still play all the games I have.
Now the question is whether the problem is only the RAM, or whether the card is also being weird, and the RAM crap was masking an additional problem. I will have to see whether there are problems operating on the good stick of RAM.