Vista - Outlook Web Access problem

I have an HP Pavillion running Vista Home Premium SP2. I often access my e-mail at work using Outlook Web Access and have had absolutely no problems until approximately 3wks ago.
Whenever I try to log on to my e-mail, using IE 8 I receive the message "Cannot Disply Webpage". If I click on the Diagnose Problem button I receive the message that my pc pinged the OWA server but received no answer. I made it a trusted site and get the same response. I have tried to log on using two other web browsers, Mozilla Firefox and Apple's Safari browser. Both tell me that they are receiving no response from the server.
Since all browsers are unable to access the web site, I assume, and, yes, I know it is dangerous to assume, that it is not a browser centered problem.
I then thought the problem might be being caused by my firewall not allowing the server response to get through.
I am running Norton Internet Security 2009. The windows Firewall is not active nor is Windows Defender.
I disabled the Norton Security Program entirely and still can't get a the pc to acknowledge a server response.
Does anyone have any thoughts on what I might try next?
I know there is nothing wrong with the OWA server since none of my co-workers are having any problems.
It worked fine for me and then just stopped. I have changed nothing on the pc. The only thing may be a windows update that automatically installed but am not sure how to check this. I am not entirely sure of the day the problem started.
Thanks for any ideas you may share with me.

ejeffries