Hi Claudia,
I can see nobody has answered your question. I don't know the answer because I'm experiencing the same. But my case is really funny. I can see the html editor but I can't make it work with most of its functions. I can turn text bold or italics or even underline it, but I can't upload images, I can't change font color, I can't insert a link and so on. The funny thing is that I can't do all these things from my laptop. If I try to do it from a different one, everything goes fine.
I must say I installed Nanogong module, filter and htmlarea and I think everything started to happen when I did so. It did woek before that. But why just in my computer? what's going wrong and the most important how can I solve this?
I've been asking for help in different threads but nobody has answered me yet, so I'm sorry Claudia I can't be of much help to you. Just try and see if that happens to you if you try to do it from another computer. Let's see if anybody is so kind to give us a hand.