MySQL is usually used in a networkless fashion -- connecting through TCP/IP is disabled, only the UNIX domain socket is allowed. If you wish to enable TCP/IP, try commenting out the "skip networking" line in your my.cnf then restarting the MySQL server.

Alternatively, if networking is not disabled, keep in mind that MySQL accounts are not just per username, they're per location as well! Each user can have multiple rows in the user table with different characteristics -- you can give the same account different permissions when logged in from different places! -- and if there's none that allows your IP, then you won't get in.