Why is my computer not recognizing my external hard drive?

Check the connections
Check the power cable, the USB cable, and the power source to make sure each is securely connected.
Try a different cable
If there are two cables available, try swapping them out, and if the cable works on a different device, try to switch it with the one you’re attempting to use.
Check the port
See if the port is working correctly by plugging in a different device into the same port.
Troubleshoot your device
Use the Device Manager to see if the device is properly listed, and uninstall devices you no longer need.
Re-enable the device
In the Device Manager, try to find the disabled device and re-enable it.
Restart your computer
Restarting your computer will reset many of your systems settings and allow your device to be recognized.