Internet Explorer 6 SP2 Cannot Find Server

When I go to a webpage (that I have visited before) or even to my home webpage, I get the entry in the Address Block – Cannot find server. Now after I click on the go arrow several times, it finally opens up the page, but it takes a long time. Any ideas what to do? I am running Symantec Client Security but I have disabled it but no change. I have various third party software running to block pop-ups but I have also disabled that, but no change. This just started & I am not sure what to do. Please help.