I cannot access the web after I downloaded Avast . . .

I have Windows Professional 2000 and I use Internet Explorer as my browser. Once I downloaded Avast, I was unable to access the web. I had to uninstall Avast to get back online to place this post. I am not computer savy. Can anyone tell me what I can do to be able to have the Avast anti-virus and firewall work on my computer? Thanks for your consideration!

What firewall are you using and are you allowing avast! access through that firewall ???

The only firewall I was using (before I uninstalled it) was the one that comes with the Avast Internet security 5.0 program. :-[