It sounds like Wayne and Jon gave you the correct answers. Wayne was basically saying to have Avast not look at AC as a virus. Adding it as an acceptable program did this. There are a few antivirus programs that do this. Why it happened out of the blue, I am not sure.
In the future, if there seems to be an issue like this, turning off your A/V and/or firewall to see if AC or any program that is not running correctly is a goo troubleshooting step. In fact, some antivirus programs such as McAfee or Symantec have to be uninstalled.
It is better to go without an antivirus program for a day and be able to use AC, than the other way around. If one does have to do that just be careful when clicking on websites and email attachments.
Once you know it is the A/V or firewall by shutting one or both off, then you go can about the actual fix.
Glad you got it working.
