I have an old external harddisk, Toshiba 320 Gb, with a USB connector that I wanted to check for contents. It did not start up when connected and I could not hear the motor spinning. After leaving it in the freezer overnight the motor spins but it is not recognized by my computer. I disassembled it and could see that the head assembly rests outside the disk but when it is powered on, the head first moves to the center of the disk, then to the periphery and finally back to the resting position. This happens every few seconds and leaving it connected overnight changed nothing. I installed smartmontools but the disk is not even recognized by my system as a /dev/sd* device and therefore not accessible to smartd (at least as far as I know it.) Any suggestions for what I could try? I am running CentOS 7. Thank you.