Run the loop-back test (see sticky).
I am trying to do this, but am stuck at step 7. "Connect the terminal application to the serial port for your board. The baud rate is irrelevant." How do I connect the terminal to the serial port when the computer already doesn't recognize the serial port?
You can't. If the PC fails to assign a serial port number to the board when you plug the board into the PC then the USB serial converter chip is not functioning, assuming you have the correct PC USB driver installed to support that board.