getting on net and security

I eventually got laptop working ok with router and was working fine so i
downloaded avast antivirus and after restarting computer it cannot find
server so i can't now get in internet. Is this because of avast? . All
connections are fine and strength is fine. Also do i need antivirus on
computer and how do i protect stuff being sent to router to stop other people
seeing what i am up to thanks
--
lachygirl