Images disapears

Hi there!
Something strange happens to our website, and I don’t even know if it’s a theme/wordpress or server problem. I just need some advice where to look for the problem. (I’m not a technician nor very skilled in web programming)

During the last week, different images have disappeared on the presentation page. Most often the Page column images, which becomes completely or partly grey. Yesterday, the slider didn’t work, and today (a good day..!) the swedish flag in the upper left doesn’t show. This is what happens in Safari. The problem is similar, but affects other images in Firefox, Opera and IE Explorer.

The url is http://hunddna.slu.se

Our IT-deparment say they haven’t made any changes to any servers what so ever. We haven’t done anything to our homepage either (not even a blog post during this period).

Any suggestions where I should look for the problem?
Thanks!
Lotta