Insert Link Box problem

Hi,
Probably this is a simple problem, but I don't know what I can do!

I use CKEditor for Joomla in my Joomla website and I use this for standard editor in frontend and administrator side. But when I click on the "Inserti Link" button, the "Inserti Link" dialog box appear with a strange format, and not appear any confirm button (see the attachment image). So I can't insert any link in my web page...

What is the problem?

Thanks