1) Check to see if the device is hidden. For this, click show hidden devices under View, then expand all the nodes under device manager. Uninstall any entries which appear grayed out, then restart. Then try plugging your external device to the computer and see if it works.
2) Make sure that in the BIOS the ports are enabled and set to 'auto'.
3) If that does not work, try installing the drivers
for your device manually.