Available themes do not show in design admin

I would like to change my theme but no themes show up in the Available Themes area in the admin Design panel. When I say no themes I mean no themes, including the default and basic themes that load with wordpress.

This problem started when I upgraded to 2.6, btw. At the time I didn’t think much of it because I didn’t want to change my theme.

Please, please don’t tell me how to upload a theme. I know how to do that and even uploaded the theme that is currently being used. If the problem was with my uploading then the two themes that come with wordpress would be available. They are not.

Thanks for any help you can give.