Anyone else ever have this problem?

Yesterday suddenly yahoo Facebook and several other sights just suddenly stopped loading all together. Every yahoo page just didn't even attempt to connect. Yet most Google sites worked fine. Even YouTube worked flawlessly. Did everything from running threw cookies and proxy setting to antivirus sweeps windows updates system restore. Ipconfig/release renew flush DNS reset modem and router but even ping and traceroute couldn't find a problem with anything nor could windows 7 find any problems with my connection. Ipconfig/all even seems normal and al pings to yahoo were successful. And yet just a few hours later the problem disappears without a trace . Disabled all explorer add on's one by one to see if i could find the problem but nothing and now the problems gone and I have no idea what the hell happened. Its quite maddening