internet connection

for some reason as of late, my computer will not let me access the internet through internet explorer or mozilla firefox. however, i am able to access the internet through aol. so i know i have a working internet connection. i have checked all my security settings and have run spyware programs, nothing. this just started happening a couple weeks ago. the only changes i have made was installing norton antivirus with a lifetime license.but from what i can tell, norton isnt blocking either of those programs. i am running windows vista. any suggestions?