Well, hosting your VST plugins and instruments on external HD is not very efficient in general. Especially on a laptop where USB is sharing processing with other hardware and power over USB is not great on laptops. Better to keep them on same HD that is running your OS and your DAW. Use you external HD for storing sound files and your recordings. Wouldn't even record to external HD, but do what you need to do.
The AudioBox connectivity may be hardware failure. It doesn't usually just disappear. Test with new USB cable and different USB connections. Test your AudioBox on another computer. Does it work or not ? If not, then assume your AudioBox is faulty and contact the Distributor in your area for repair.
You might also try using a new power supply.
Use this article to fully remove installed device drivers. Then install current Universal Control v2.2. Once installed, open Universal Control and Update Firmware if prompted.
If you still have trouble, contact PreSonus Support for further assistance.