I did a re-install.
I configured based on this page, before:
http://www.winhelp.us/configure-avast-free-antivirus.html
http://www.winhelp.us/configure-avast-free-antivirus/configure-avast-free-antivirus-page-2.html
I’m going to try leaving off some of the extra scanning suggested, and use the defaults. Maybe that will help.