If you're using windows, you can open up a dos 
prompt and run the command "tracert 
www.sitename.com" to see the route that your 
computer takes to get to a site.  If you can't 
get to a site, it'll generally hang somewhere 
along the way -- wherever it hands is likely to 
be the culprit for why you can't connect.  From 
what you've described, most likely it's 
Earthlink.  Having traceroute information when 
you call/email is generally helpful (assuming you 
can get in contact with anyone at your ISP who 
knows what they're doing).