The operating system is fine. I keep it updated and access the internet primarily through a user account, not the administrator account, so the probability of anything happening to the operating system is very remote. Erasing the hard drive and reinstalling the operating system would be an excessive solution.
The only warning was Avast suddenly said my computer was no longer protected. From that point on Avast did not work in any way. I check avast once a month to see if an update is available, so I would have had the September update. So, this meant an uninstall and reinstall. I did a clean reinstall with the uninstall utility (avastclear.exe). My frustration is that this is the second time this has happened in the past month. It takes about a half hour to uninstall and reinstall, including three restarts for the uninstall, the reinstall, and restoring the settings. It's such a waste of time.