Keyboard fiddling didn’t accomplish anything. Suspicion has now turned to the battery/power system.
Battery life on this machine, an Acer Aspire 3000, has always been lousy. It also rapidly got worse. The battery life dropped noticably within three months of purchase, and by nine months from purchase the battery life was under ten minutes, meaning the computer couldn’t really run without a power cord any more.
When the system is freezing up, I’ve started fiddling with things and several times triggered a “Not Responding” message from the power management program. This also somewhat ties to the system only working if I let the bettery drain completely before bootup. Makes me think the system is freaking out because the battery is always showing a critically low state, and it isn’t charging.
Sadly, a new battery appears to cost $150. I’m really not sure if I think this computer is worth that, even less than a year old. Given past experience, I’m certain the new battery will just dwindle and die again in the course of a year or so anyhow. Might be easier to make do with a computer that has to be unplugged to turn it off, since I’m far from certain a new battery would solve the problem. Have to keep tinkering.
Edit: further tinkering supports the wacky-battery hypothesis. Restarting with no battery at all in machine works fine. I ordered a third-party replacement battery, rather than one from Acer; hopefully the quality will be a bit higher. Would be nice to be able to run without a wall outlet again.