Along the top of the chat window click the "Friends" tab and scroll it to "Paragon Chat". If "Paragon Chat" doesn't show up in your "Friends" list, you are either running Paragon Chat in offline mode, or running Icon instead of Paragon Chat.
If "Paragon Chat" does show up in your "Friends" list, go to the "Chat" chat window (by the "Global" and "Help" windows) and right click in the middle of the "Chat" chat window and click "Edit Tab". "Paragon Chat" should be in the list on the left. If not, move it from the list on the right to the list on the left and hit "ok". Then, in the box where you type in text to chat to people, type "/chat_set Paragon Chat". Now chat away, someone should reply.
If "Paragon Chat" is not in your "Friends" list, that will take a lot more help here. Let us know.