One thing to look for is whether PASV mode is turned on. Typically if your firewall is blocking active FTP, you'll be able to log in, but when you attempt to get a directory listing, it will just hang.
You don't say what FTP client program you are using, but the following should work for IE:
http://compnetworking.about.com/cs/novellgroupwise/ht/setpassiveftpie.htm
