Seeking expert advice on difficult internet question

This is a difficult question that has everybody stumped so far. I think there's an obvious answer and I don't see it. Is there a checklist of things I should be checking or resetting for a problem like this? I'm using Vista on a Lenovo T500 with Norton 360.

I can access anything on the internet except one site - I get timed out every time I try to open it. It is my bank site (accountonline) and I've been accessing it for years without any problem. I usually use Firefox, but, starting 3 days ago when it began showing the "the connection has timed out" message, I tried with other browsers - IE9, Opera and Chrome. They all do the same thing, able to access all websites except that one. Using my wife's laptop the website opens immediately! And that's using the same router. I talked to several bank customer service people and to the website's tech people in Florida and India. So far no answer.

I've tried turning off Norton firewall and antivirus - doesn't change anything.

Won't ping - "Request timed out." I tried a route trace and it goes through to the 17th hop (a citibank server in either Houston or Dallas) then times out over and over. I reset my router on the off chance that would work, but no change. I tried turning off my wifi and plugging in via ethernet cable - no change. Tech support for accountonline.com tried setting up my IE9 to work (multiple sundry setting changes) but still couldn't access it.

So it doesn't seem like it could be something set wrong in a browser because none of the four work. And it can't be the website or the router because I can access it with another computer. It has to be in my machine. Something in my laptop causes a Texas router to not accept it. What could be causing this?

Any suggestions appreciated, especially a troubleshoot checklist for a problem like this or a suggestion of what could be set wrong or busted in my laptop.

Ben