Sorry for the long absence. My sound card suffered a mysterious fault, rendering the system unusable for weeks before I identified the problem. So I replaced it, restored my installation, reinstalled drivers, and everything started working again.
Well, except my mysterious spontaneous crashes. And my avast! weirdness.
DavidR, rhuds13... I'd try another firewall, but disabling and uninstalling ZoneAlarm did nothing to alleviate the problem. I don't see why installing a different one in its place is going to help.
No, the problem is avast!... or some other program that it's conflicting with that I haven't considered yet. The thing is, it's only been doing this for, say, a month. And my laptop, which shares my desktop's security setup (ZA, avast!, WinPatrol, HijackThis, Ad-Aware, etc. etc.) does not have any of these issues.
Is there a log file that I should be reading or posting? Anything that would help?