Logical damage of seagate disk due to long time of use and go corrupted all of sudden.Power failure that made damage to the hard drive.Virus infection that brought the seagate external drive not recognized.There are many possible reasons that may explain why your hard drive is not showing up or detected, and the most frequent causes may come from the following. Seagate external cannot be detected or recognized and won't show in PC NOTE: The solution for unrecognized seagate hard drive also applies to other brands of external hard drive like toshiba, samsung, wd. Steps to fix the Seagate external hard drive cannot be detected.Recover data from undetected/unrecognized seagate external hard drive.How to fix Seagate external hard drive cannot be recognized?.Situation 2: Seagatexternal hard drive cannot be detected in Windows 7/8/10 but showing in Disk Management.