Take your external drive out, if its 3.5 drive with sata connector, hook it up to your desktop, check it in bios to make sure it comes up.
If so put the drive back inside the enclosure, next check your usb wires, make sure there is no slent or cuts on the cable.
If so that is part of the problem with it not showing up in windows, if the cable is fine, plug it up and boot into windows.
Pull up the device manager and check the usb connections, it should appear under a certain name,
If it does not check and see if windows may have a exclamation by it and says unknown usb device.