4.3 has some bugs in it. I recommend 4.2 SP2. I'm not sure that will fix your problem, though. Are you plugging in directly to the computer? You're not plugging into some kind of hub? Also, try changing themes. I've run into issues where some themes don't want to allow the device to connect to the DM. It's rare but I've seen it happen. It's possible that your device has a bad USB Port. Does the BB charge when plugged into the computer?