Unable to connect to port 21

For some reason I am unable to connect to anywhere on
port 21. I know the ip i'm trying to connect to (my web
site) is up because I can get to it from friends
computers and from work. I can ping the computer and
connect to it on any other port, just port 21 won't work.
It won't work on anywhere I try to connect. I have
Comcast Cable for my internet and I run no anti-virus or
firewall software (including the windows ones) and my ISP
refuses to admit they block my outgoing port 21. Anyone
have any idea what could be blocking my outgoing
connections to port 21?