403 error when activating themes

Hello,

I’m looking for help activating themes.

I have wp succsessfully installed but cannot see the themes.

When I look at the preview of the classic or default-theme I get error 403, forbidden, when I activate one of the two again I get error 403 on my url http://www.feuerartistik.com

I tried other themes (uploaded correctly) but with the same result..

I would be highly gratful for any help, as I would love to start working with wordpress..

thanks in advance