First you need to locate the issue.

try the drive with another usb cable. (checking cable integrity)

try the drive on another computer. (is the drive faulty)


if issue not found try clearing the hard drive buffer, (power down computer, unplug hdd usb cable and power down the hdd. wait 10 seconds, power up the computer, when fully booted power up hdd, wait a further 10 seconds and connect usb cable. look for hdd in disk management