I assume that the drive is not recognized by Disk Management but by Device Manager. Am I right?
If this is the case, my suggestion would be to attach the drive to another computer and see if it would get recognized by Disk Management. That way you will be sure if there's something wrong with your computer or the HDD itself.
In case the issue persists, then there could be something wrong with the drive. It may be a good idea to contact the place you got it from.
i have a external hard disk which is not detect on my pc. i have try Disk Management & Device Manager, but also cannot detect my hard disk. wonder still got any solutions which can help me? (the data inside external hard disk is important for me) thanks