I suppose if all this doesn’t work for you, you can go back to using 4.8? You said that there wasn’t any problems prior to installing 6.0 , so if this works for you, here is the link:
http://www.avast.com/en-ca/download-software#tab2

You can additionally try installing avast 5.0 and see if this helps.

Have A Good Day (^.-)~*