I have a Dell PowerConnect 7048 with 48 PCs connected to it. There is one particular URL that I cannot ping or browse from any PC. Every other URL/Site works without any problem.
I plugged five of the 48 PCs direct into the router and the URL worked fine. So it is not the PC, DNS, ACL, blacklist or IE settings.
I dont have any proxy in my network. I think the problem is in the switch, which by the way has no Vlans or any other configuration. It is pretty much the factory settings.