port 80 closed?

[Park5]

Hi

I have Microsft Small Business Server 2000 and a possible ISA firewall problem.

Iv'e been using a web based Citrix Program which uses port 80. I have been using this program for a few months with no problems.
Recently I tried to run the program and it wouldn't connect.
The software company's website says to try a telnet command from the command line: telnet xxx.xxx.xxx.xxx 80.
When I did this I got a message saying 'could not open a connection to host on port 80 : connection failed'

Is there a way to open the port in ISA etc or does my problem lie somewhere else?

any ideas welcome

Thanks