Thank you, Tech. The slow closing stopped. 8 months or so ago, when I had the same problem, and had a MS-certified tech who'd proved expert before look at it, he worked for two hours. even speaking to other professional techs. The problem remained. He could have reinstalled XP, but doesn't like to give up. He left to do more research. When he phoned, 30 minutes later, Windows was closing normally. He said he hadn't fixed it, didn't know what the cause was. (I'm hoping it doesn't recurr.) AVAST, of course, is innocent in both occurrences.
"Updates" was corrected, though I had to sent MS Support a couple of reminders that they hadn't sent the follow-up email with the fix. It was a corrupted Windows Update cache folder.
I am very pleased with AVAST. It's magnitudes more reliable than Trend Micro PC-Cillin, which it replaced, is more user-friendly than any other AV I've owned (a lot). You people on its forum are newbie-tolerant (not all forums are) and generous. Thank you.