Thickbox.css

Lately I’m not able to add media content to my blogs anymore. When click one of the media buttons, the thickbox popup doesn’t show. Instead it appears undertneath my page. I know that this happens when the thickbox.css isn’t included properly. I looked up the location of this file and it appears to be in the right directory. When I link to it directly however, I don’t get to see my .css file.

Also when i edit my blog posts, my text is white on a white textarea so i can’t see it. When I toggle through html and visual it’s black again.

Does anyone know what to do to solve this problem?

Thanks in advance,
Rick