My Memorex double layer 16X dvd burner won't connect to my mac even though it used to all the time. It turns on and when i plug it in via the usb port the mac won't pick it up. The light flashes on the device when i plug it into the usb so i know that its doing something but it won't work on the mac. Its not the usb port, because other things i plug into it work just fine. Any idea why this is happening?