There are certain factors which prevent IdentD from responding. Most commonly firewalls will stop this, and if you have Windows XP it's likely you have the XP Personal Firewall enabled without realising it. Check out
these instructions to learn how to disable it. Basically, you need to make sure IdentD is on as Guyvah said, use
/identd on and make sure port 113 is free.
Routers also cause issues (due to the NAT firewall), as can DSL connections. The best thing to do would be to contact your router manufacturer or ISP respectively, either by email or phone etc, or, in the case of the former, read any manuals that came with it.
DALnet's Exploits team wrote a useful
Ident FAQ which you may like to browse.
You can also try running a
Search for "ident" or "identd" for more results. Expand to 'All Forums' and expand the date range to 'All Posts' for best results.
G'luck!
Regards,