Things to Try When the Computer Won’t Recognize Your USB Device
1) Try connecting to other USB ports on the PC. If currently connected in the front USB jacks of a desktop pc, try the ones on the rear panel.
2) If connected thru a hub, try connecting directly to the pc. Move low priority devices like printers etc. to the hub where they normally operate well.
3) If none of the above works reinstall the USB driver. The latest drivers are located here http://download.yamaha.com/usb_midi/
4) Try changing the USB cable to a new one.