One way to diagnose if a dns problem.
whois xbox.com
grab the nameservers from the whois.
In this case:
ns3.msft.net
ns4.msft.net
ns1.msft.net
ns2.msft.net
ns5.msft.net
nslookup
server ns1.msft.net (etc.)
xbox.com
www.xbox.com
msft.net
...etc.
In this case ns1.msft.net doesn't even answer consequently you will not be able to get any addresses for the other domains.
If you query your local isp dns (or google at 8.8.8.8 or 8.8.4.4) it's possible they have the addresses cached and will return something.
But if the dns isn't answering (per the whois) you have at the very least a dns issue.
While I was typing this ns1.msft.net started to answer again...when I started the "server ns1.msft.net" part failed.