On my Mac, the external hard drive on which I have already made several backups is displayed with a triangle and a thick bar underneath. If I try to click on it, the hard drive disappears from the computer and I have to plug it in again. And all backups are hidden. However, the storage space is still occupied, which I can see when I call up the "Information". How can I fix this mishap? Thank you very much. Lutz Hanisch