Haven't been able to figure this one out. Sometimes our workstation will stop accessing the internet. You can ping, and do all of that just fine, but when the proxy address and port are enable in IE8/Firefox, it just sits there loading the page, but never does. If you disable the proxy, then it will begin loading pages so it's proxy settings specific.

This is only for the problem machines. There's 1100+ other stations that use the proxy fine.