First test your account in your browser. If your password contains special characters (including - or _), please change it.

Enable the option "Enable Premium globally" in the Premium menu.

Allow java and javaw in your firewall and virus software. Disable (or un-install) the html/web download scanner in your virus software.

Then remove your account, restart jD, and add the account again.

If this wouldn't work, please provide a complete and detailed log.