“This page cannot be displayed”

Since installing Norton AntiVirus I cannot get the page to come up that allows me to “buy” or “order”. I get “This page cannot be displayed.” When I remove the Norton AntiVirus all is almost all well. Just those pages that are under revision or some other problem do not come up. What must I do? I have done the “refresh” thing. And I have no idea what the settings should be.