Hi I have a Musical Keyboard (Korg Microkey 37 usb powered and doesnt need any drivers) and my Macbook Pro Mid 2012 cannot recognize it any more. it doesnt work on any of booth ports if i plug it directly, i have tried differents usb cables and nothing. But if use an USB MultiHub (usb powered) it works. Why? it used to work on both ports but they stopped to recognize it. first in one port and several month after on the other. by now is the only device that i have noticed this I have tried resetting the PVRAM (cmd+opt+P+R) and nothing. any suggestions?