I tried two new themes from the http://themes.wordpress.net/ list, downloaded, unzipped and then uploaded into my site's directory wp-content/themes/ and into folders named the same as the theme name.
When I do to the dashboard I see both of them and the editor lists their files once I select either one. But when I click view site the page comes up blank. Switching back to the other theme i have been using - one called pool that came as one of the defaults - eveything is fine. I have switched to other default themes and they all work but these two called Greenart-10 and Oceanbech-10 don't.