I found it a simple matter to open a panel on the bottom of the laptop and clean out the accumulation of lint I found in the heat-sink.

But although a cooler CPU certainly couldn't hurt and may indeed extend the life of this machine, I later found something else that I now think is the real cause of my troubles. I noticed that the icon for AVG had an animation moving almost all the time. Its control center interface came up slowly (as has most all programs) and I saw that the Updater had been running since I'd started the computer over five hours earlier. Then, I found that the updater had been denied access to the internet by ZoneAlarm. Despite the agonizingly slow response, I finally was able to disable the automatic update in AVG, and after rebooting, have seen a wonderful improvement in response time.

I'll certainly report back in a couple of days, but for now it looks to me as though my problem was extra-slow response due to the thrashing of AVG update. I am wondering if I'll have to re-install AVG or ZoneAlarm (or both) to allow regular updates.