If your external drive is correctly configured, plugged in properly and is not being detected at all.
Remove and reinstall all USB controllers
To remove and reinstall all USB controllers, follow these steps:
Click Start, click Run, type sysdm.cpl in the Open box, and then click OK.
Click the Hardware tab.
Click the Device Manager button.
Expand Universal Serial Bus controllers.
Right-click every device under the Universal Serial Bus controllers node, and then click Uninstall to remove them one at a time.
Restart the computer, and then reinstall the USB controllers.
Plug in the removable USB storage device, and then test to make sure that the issue is resolved.
If you have any error messages when you insert the USB stick let us know what they are.