Portable Internet connectivity problem for Vista?

I have DSL from AT & T and connect the yellow Ethernet cable to my laptop. My Web works well when you turn it on, but after 30 minutes or less, a pop up message saying Internet resident proxy stopped working. I use problematic Internet Explorer Diagnostic regard, I offer solutions, try them all, but none works. The same happens when you hibernate the computer, then switch back. I have to reboot and then it works fine. I called AT & T and there is absolutely nothing wrong on the internet. It is a problem with my network adapter. I called Toshiba, but have a very poor support system and the call is dropped and I do not really want them to call again. Please help me. My problem is my Internet connection has no connectivity / shortly after using the Internet for a while. I use Vista. The problem is probably with the network adapter. Please help. Thanks!

Start here. Good Luck