Modal window shows wrong

Hi,
I'm experiencing an issue with the media browser, actually I cannot upload and show correctly a media file.
When clicking on the Select media button the modal window doesn't just have the media block but also everything of the site (including the admin menu) and it's not available a close button to close the modal.
Furthermore, when I upload a file, there's a message which confirms the upload was successful but the modal close and reopen itself. If I click cancel to close the modal window I see nothing in the Select media placeholder.
So basically I cannot upload any media.
Hope you can give a hint

Regards