Remove the media card and see if it still works. If it does (dont restart anymore), then think of what are the files u placed in the media card before the problems happened. remove those files from the media card. It should be fine after that. If not, back up all your files and reformat the media card via the blackberry then put the files back slowly.
Oh yes. i had the problem last week. But the above steps fixed it. OS: 184.108.40.206