The following is troubleshooting information in the event the TD-50 does appear as a selectable device within the computer.
-- Be sure the correct drivers have been installed in the computer. You can find the current TD-50 drivers available on the Rolandus website here:
https://www.roland.com/us/products/td-50/downloads/
-- After installing the drivers, be sure to select "Vendor" in the TD-50 for the Driver Mode: (SETUP > USB AUDIO[F2] > Driver Mode). "Generic" Mode is the factory setting. If you need to change it, be sure to cycle the TD-50's power Off and then On again after doing so.
-- Do not connect to a USB "hub," but rather a physical USB port on the computer.
-- Use only an (A-B) USB 2.0 cable. USB 3.0 cables or USB 3.0 computer ports without backwards compatibility are not supported.
-- The use of USB cables longer than 15 feet and/or USB repeaters may affect the USB connection and functionality and are not recommended.
-- Check the USB connection on the side panel of the TD-50 to make sure the USB cable is inserted completely and securely.
-- Disconnect any other USB devices (except for the computer's keyboard and mouse) from the computer. This includes an audio or MIDI Interface that may be connected.
-- Close and/or shut down any system monitoring/anti-virus software while troubleshooting.
-- Try a different USB cable, along with different USB ports on the computer.
-- Reboot both the TD-50 and the computer.