I can’t activate themes

Hi, I’m trying some templates, specially one that seems to work well but I cannot activate it. Nor this neither any other, including the one I was using during all this time. When I go to see a template (Technology Computer WordPress Theme) in aspect, by clicking on it it opens up in a complete page, without the option of closing or activate it. It happens with all the themes, I cannot find the way to change one theme for another different from the actual one. I’ve been just adapting one with the help of the plugin “theme test drive”, but nothing happens. I’ve desactivated the plugin to see if it worked, but it didn’t. I’ve tried with different browsers but there’s no way the make the change.

Any suggestion? How can I chage it in the database?

The site is: http://www.elespinar.info/blog

Thanks in advance, Peter Louis.