Problem with uploading media

Hi,
I have a problem uploading media. When i upload something i get an error saying there was a problem with the upload, and it does not matter if i upload with the multi file uploader or the other one. When i go to the media library however, the things i tried uploading are there, but i can not use any of them since when i try to put them in a post or make them the background for my blog they can not be seen in the library, and i get the error again when i try to upload them. How do i fix this?

Please help me with this, i am very new at all of it.

My blog is: http://skola.femblogg.se.preview.binero.se