Image uploading problems

Hi all. I have looked through the image uploading sticky, but it does not address or resolve my problem. I have the version 2.6 of WP MU, and the add media icons are not all showing up. I do have a grey star-like icon, but no photo icon or any of the others. Furthermore, when I click on the one add media icon a blank page comes up – nothing.

I have tried this on both mac and pc, as well as Firefox and Internet Explorer and still no luck. Has anyone had a problem like this? Any ideas? Thanks.