I'm not sure what your problem is Arcormacolindˇva, it depends on what browser you are using, if it's Internet Explorer (4 or above) then it should be fine, as long as you have Java enabled. If you are using Mozilla, then there is a seperate Java program that you need to download, the inbuilt help should direct you to the right page. Other than that, there could be more problems with the chat server, and the fault may not lie at your end. Hope I've helped a little, and welcome to PT, I hope you aren't put off by a disgruntled server.
Other than that, you might find help in the thread "chat problems" under "website news". But I think Plastic has helped you along the way already.