Question about Outlook Express

I am volunteering for a local teen center trying to fix an issue retrieving email through Outlook from TWC Road Runner email.  The network and email setups are all new, but both were communicating appropriately prior to last week.  TWC says it's a firewall issue.  I have, along with help from the company who set up the network, tried to troubleshoot just about every setting but cannot correct the problem.  All cookies, cached files, etc. have been dumped.

The issue lies with connecting to the TWC webmail site.  I cannot get to it via internet explorer at webmail.roadrunner.com.  I get the mesage:

Internet Explorer cannot display the webpage.

This problem can be caused by a variety of issues, including:

• Internet connectivity has been lost.
• The website is temporarily unavailable.
• The Domain Name Server (DNS) is not reachable.
• The Domain Name Server (DNS) does not have a listing for the website's domain.
• There might be a typing error in the address.
• If this is an HTTPS (secure) address, click Tools, click Internet Options, click Advanced, and check to be sure the SSL and TLS protocols are enabled under the security section.

I have used IE 8 and 10 as well as firefox and google.  None of the 4 computers on this network, or any linked into the internet service here, can reach the website.  From my wireless phone, I can reach the webpage, but with security certificate issues. 

Any suggestions are welcome.  I have exhausted my limited expertise.  I am beginning to think there is some malware causing this.

Cheers!