unable to acces sites using IE6 or Nscp

I can not log in to Msn.com, my.msn.com,Iowastudentloan.org,signingagent.org and a few others. When ever I go to these sites with IE or netscape I get the page can not be reached or operation timed out. I am using Win xp and this coputer is hooked up to a router that is using mediacom cable internet access. If I go to the other computers in my office that are hooked up to the same router I can get to these sites.I need some help, I have already changed all the IE settings around and that has not worked.