I met the same problem many times. Sometimes when I tried to launch msn to test my website, it's unreachable, sometimes live.com will be working, sometimes not. But 2 hours later, msn.com and live.com will come back to normal. Same problem with yahoo, the frequency is lower than msn.
Maybe just an ISP problem reaching their servers. I happened quite a few times to be unable to load a website while others I had on MSN were testing it just fine. Don't really think names like MSN or Yahoo would not do anything to avoid downtime.
maybe as stated above some ISP problem, or try to clear your browser cache and cookies then try again