AVG scan showed no infections.
Spybot S&D scan showed no infections.
Ad-Aware scan showed no infections.
I did some Googling and happened upon this forum, among other sites.
I downloaded and ran (in order) ComboFix, VundoFix, and MBAM. ComboFix seemed to remove a few randomly-named DLLs. VundoFix did absolutely nothing. MBAM detected one instance of Vundo and claims to have removed it.
Since a reboot, I am not getting any more pop-up ads. However, I am still unable to re-enable Automatic Updates. I suspect that the virus corrupted or removed some system files related to AU.
DDS logs are attached. HJT log is also attached.
Thanks so much!