I recently installed Avast Free 15 and, after a few days, its shields shut off. I tried to re-establish them with no luck, so I uninstalled the program and reinstalled Build 2015.10.0.2208. I don’t know which version I had installed about a week ago, and don’t know if the shield problem was a one-off incident nor what might have caused it to occur. So far, it hasn’t recurred, and Avast Free’s as well as a recent Malwarebytes’ scans do not reveal any malware, so I hope the problem has been cured. I would like to know, though, if anyone has heard or experienced any similar behavior, or might have a suggestion as to what happened. Thanks.
I recently installed Avast Free 15...............what AV did you use before installing avast? did you uninstall it before installing avast? did you use that vendors removel tool to clear all leftover files?
Thanks for the reply… I had EsetNOD32’s latest version installed, and used its Uninstaller and Revo’s uninstall program to clean up any remains. I also did a full manual examination to ensure there weren’t any remnants lurking in the Registry. I should also mention that I’m running Windows 7 (fully updated) on a dual boot (With XP) using TinyWall with Windows Firewall for protection. I also have Malwarebytes running for real time protection. I just hope this is some kind of abnormality.
if it happens again try avast repair…
controlpanel > ad/remove programs > avast > uninstall/change > repair option …
Thanks for the tip, Pondus. I will certainly keep that in mind as I wasn’t aware you could do that through the control panel (at 75, I can still learn something new every day). 
your wellcome
removal tools for AV found here https://singularlabs.com/uninstallers/security-software/
and here https://www.avast.com/en-eu/faq.php?article=AVKB11#artTitle
avast FAQ http://www.avast.com/en-eu/faq.php
FAQ videos http://www.avast.com/en-eu/faq.php?q=video#searchForm
My problem is that the Avast videos is that they all use the default install. Something most of us do not use.