I have a Seagate 500GB Momentus 7200 harddrive which I was using as my internal bootdrive. I have replaced this with a Samsung SSD 850 EVO 1TB harddrive. I now want to connect my old Seagate as an external via USB to copy my old files to the new harddrive, but the drive just won't show up anywhere (also not in Disk Utility). But if I switch the drives again, my Macbook still boots just fine from the Seagate. So it just won't read it as an external. I've tried different cables. Why won't it recognize it?