All internal memory is gone
 

I've been a happy N900 user since December, but today something strange has happened. I noticed my background picture was gone and almost none of my programs would work. I get the message "operation was deactivated temporarily because of lack of memory" (translated from Norwegian).
When checking my memory it says I have a total of 455,8 mb of memory. What happened to the rest? I cannot connect to the pc to check usin mass storage mode, and all my music and video files are gone.
Anyone know what is wrong?