If it`s not seen at all in the Device Manager,then either the cable/plug have worked loose,or the drive is dead.
If the Device Manager sees it,but says it has a problem,then uninstall/remove the device,from the Device Manager and restart.
If you turn the computer back on and the device has not automatically fixed itself,then manually
re-install it via the add new hardware wizard.
If that doesn`t work,the next poster might help.