can't connect to internet

i have installed avast 4.8 but i have a problem with it i could not connect to internet i am using dial up connection every time when i try to connect answer is the same remote computer did not respond if some how conection is estableshed after some time it disconects and when i uninstalled avast on first try i was on . i have scanned computer no virus was found can any solve this problem

What OS are you using?

Are you using a firewall?

Do you have any other antivirus in this computer? Did you have one in the past? If so, how did you remove it?