@angelagscott in case the issue with the OS upgrade if the hard drive is indeed detected by another mac
@angelagscott try powering off the computer and leaving it off for 1 minute without power, same with the hard drive and try again
@angelagscott is the hard drive detected by another mac using an earlier version of the OS like Yosemite or Mavericks?
@BigBadBiker does the drive power on with another power adapter of equal voltage and amps?