Steps you should take:-

1. Do you have a web connection?
2. You may have a connection, but a router has failed and this can result in a block to the mail server.
   The easiest way to check this is to PING your domain name
   Goto DOS and type ping www.yourdomainname.com and see if the server is responding.
   Please note:- depending on what ISP providoer you connect through means there will be different paths taken to get to the server.
3. Are your pop3 settings correct?
4. If you have just shifted your domain from another web hosting providor
   It takes about 24/48 hours for name servers to propogate - often it's just a case of waiting until this happens.
5. Sometimes it's possible for a mail lock to happen, especially if your computer has crashed.
   If this happens please submit a support ticket or contact NZservers for the mail lock to be cleared.