i have a 500GB external HDD attached on my Mac Mini as download drive (USB 3.0). The drive works fine I am sure of. Now here is the problem: every time after cold boot, Mac Mini just won't see my attached external HDD. Open Disk Utility, see nothing. Unplug and plug into the SAME usb port, still won't see. I HAVE to plug into different USB port, then the Mac Mini will see the drive. The Mac Mini is 2011 model running Mountain Lion 10.8.4.