Help!!

My father-in-law's desktop computer hard drive died. Not only died, literally smoked. He got another and it works fine except it won't go to Yahoo. I took it back to factory, uninstalled Norton, set privacy levels as low as possible, disabled windows firewall, get IE can't display the page. The real pisser is I can unplug his ethernet cable and plug it into my laptop that is set up the same way and it pulls up fine. We took the computer back to Best Buy and they plugged it into their network and it pulled up fine. I'm going to try changing the DNS to a public DNS server tonight and flushing the DNS. Also, since he and I have the same ISP, I'm going to take my spare DSL modem configured with my info and connect it to his phone line and try that but none of that should make a difference, right? I've googled the issue but seems nobody else has had this problem. If none of this works tonight I'm at a loss. Ideas, comments, name calling?

By the way, also disabled the firewall in his DSL modem.  Tonight I'm also going to set the modem to bridge mode and authenticate through his pc