I can query the nameserver from the nameserver but not from other machines. Why?

This may be the result of the firewall configuration stopping the queries and/or the replies. Also check the 'allow-query', 'allow-recursion', 'allow-query-cache' options, as well as any 'listen-on' statements, in your nameserver's configuration. The default settings can be confirmed for your version of BIND by checking the Administrator Reference Manual.