No stylesheet in TinyMce

Dear WordPressers,

I am using the TinyMce Advanced editor. So far everything works fine. Except on one computer. Here the stylesheet drop down doesn’t work. It doesn’t show my custom made stylesheets. At this computer IE8 and Firefox is being used. I tested it on several other computers with the same and other browsers and it always worked fine. But not on this one computer. And that is the most important for editing. I have also the problem in Safari, but that wouldn’t be so important. A good functionality for IE and Firefox would be great.

Has anybod an idea why this happens?

Would be nice to here some good ideas.

Thank’s a lot for answering!