External hard drive not detected or recognised

[merlin]

check your external harddisk with command fdisk -l
if your device detect, try create a new partition with this command cfdisk /dev/sdX (sdX is your drive on result from fdisk -l)
try to mount your harddisk, this is step:
1. Open your terminal and create folder usb in directory /media
# mkdir /media/usb

2. Then, try mounting your harddisk with below command:
# mount -t ntfs /dev/sdX /media/usb

3. If success, try open directory /media/usb

Hope this help!

Regards