I had this happen to me one time and the issue was that I setup static IPs for my PCs, only to discover that I had given the same IP to 2 of the PCs, therefore causing your situation. It's a shot in the dark...hope it works.
I have two notebooks, one Packard Bell Easynote and the other a Fujisu Lifebook, each operating with XP Home. I wish to be able to share broadband access simultaneously. The wireless router is an Orinoco BG2000. Either of the laptops can connect independantly, but not at the same time. Can anyone help?