A few weeks back, I installed a new external for Time Machine backups. I've since run numerous back ups, but recently, after restarting my iMac due to it freezing, Time Machine now says Backups: None... As if I've never run a back up. What's more odd, the external is there, but what was once a 1.5TB driver now only shows 300GB available. So there's definitely data there... But how do I reconnect to the previous Time Machine Backups and continue where I left off??