If you've come here to report a problem with HotCat, please notice that it will be much easier for us to help you if you give a detailed description of your problem. Just stating "it doesn't work" doesn't help us much to help you.
Hints on how to report a problem
Be specific. Do tell what exactly doesn't work. Do you see the "(+)"/"(–)"/etc. links after the categories? If not, say so. Otherwise, what exactly isn't working when you click those links? Are you getting suggestions when trying to add or change a category? Can you save? If you can save, is the edit saved correctly?
Does the problem appear on any page, or only on specific pages? If the latter, which ones?
What skin (vector, monobook, modern, other?) are you using? What browser, including its version, and what operating system are you using?
Most browsers have some "error console" window where they display error messages if and when something goes wrong. Take a look at your browser's error console. Are there any JavaScript-related messages? If so, what do they say?
Telling us these things already goes a long way at finding the root of the problem. If you omit this information, chances are that we'll have to ask you about it anyway later on.