Cannot Access Yahoo

After uninstalling Avast I can go to www.yahoo.com and mail.yahoo.com, however as soon as I re-installed Avast those pages time out. When I ping yahoo.com, it times out. This is the reason why I initially uninstalled avast. Any ideas?

Which firewall do you use?
Which is your operational system?
Do you have any other antivirus in your computer?
Which browser do you use?