Help! Theme preview and blog display seem corrupt

This is probably a very silly question, but most of the themes that I install doesn’t display properly, and neither does the blog. When I look at the page with installed themes, all themes except Twenty Ten don’t have any pictures (it looks like the link is broken por similar) and when I activate one of those themes and view the blog, it displays only text and no pics or theme formats. I’ve tried Chrome, Firefox and IE, same thing in all of them.

I recently migrated to a new (Win) computer, on my old one, the themes displayed correctly. I’m thinking that I need to install something, but on the other hand, the readers wouldn’t have to do that — so what’s wrong? The blog is hosted on a Swedish commercial web hotel.

Many thanks in advance for any tips! (I guess I don’t need to tell you that I am new to this …)

/G?rel