I use an external hard drive for my time machine backups on my iMac. Recently Time Machine stopped working (exclamation point on the TM icon) and it says Backup Delayed. I don't see the external hard drive on my desktop and can't remember if I used to. I did try connecting it to another computer (MBA) and still didn't see it show up on the desktop. I can hear the drive spin up when it is connected. I can see it in my Disk Utility (both verify and repair disk are available). For the mount point it says "not mounted". Can somebody recommend what steps I should take to try and fix this issue? I'd prefer not to have to format it (and lose all my old TM backups but I will if that is necessary. If this is a sign of hard drive failure I guess it would be better to just get a new one rather than trying to repair it since this is a drive to backup my whole computer. Any help would be appreciated. Thanks.