system
6
Not sure whom to address…did you two guys have previous A/Vs on the machine ?..eg. AVG, etc.
I ask because perhaps you have been using Avast for awhile but initially had an other A/V.
Besides a clean un-install and re-install you need to make sure you truly remove all remnants of old A/Vs.
Avast and these old remnants can have conflicts: http://www.avast.com/faq.php?article=AVKB11#artTitle
Also, not knowing your PCs you should look/post other security software you have…any that came with machine, etc.