I had this problem on WinME, and I fixed it by running the internet connection wizard, and filling in the same account details. It reset whatever the problem setting was, and it was OK after that.
Until, that is, I stopped using the network and went back to my modem. I hadn't altered the dialup settings but it wouldn't show pages, just as you describe. That suggests it's something in Network control panel that's causing IE to play up. I even reset IE's web settings, and tried Netscape, but still no joy. Winamp couldn't access the CDDB.
Maybe remove and reinstall Client For Microsoft Networks (or XP's equivalent)?? Shouldn't happen right after a reformat.