Computer not recognizing external reformatted hard drive?

If you unplug the usb cord and the information disappears from the screen in disk management it is pretty clear that that is your external drive. If there is not data on it there is no harm in initializing it or doing another format. I agree with your friend go to Control Panel > Admin Tools > Computer Management >Storage >Disk Management > locate external usb drive. ign a drive letter to the external drive. Sometimes the drive letters get messed up and you have to manually ign a drive letter. Usually better to use the letter J or higher so that when plugging and unplugging the usb drive the computer will not miss name it.