You may see more than one com port listed in the tool/serial port menu, but only one com port will work to give you the output from the board. you can not set the comport for the Arduino to any vacant or not in used port. If you do not select the correct port you will not see anything on the serial monitor.
The only valid port for you is the com port that shows the correct values on the serial monitor for your board... Which com port selected from the tool/serial port menu gives you the correct output on the serial monitor?