Explorer: This website cannot be displayedFirefox: Server not found. Firefox can't find the server at www.xyz.comChrome: This webpage is not available. The server at www.xyz.com can't be found, because DNS lookup failed. DNS is the network service that translates a website's name to its Internet address. This error is most often caused by having no connection to the internet or a misconfigured network. It can also be caused by an unresponsive DNS server or a firewall preventing Google Chrome from accesing the network. Error code: DNS_PROBE_FINISHED_NXDOMAIN
It seems like you are having DNS problems. First thing I would do is try clearing your DNS cache:
If that does not help, then try changing your DNS servers temporarily to Google's (220.127.116.11 and 18.104.22.168) just to make sure that the DNS server that you are using is not having problems.
To do this on windows 7: