1. First, make sure that the serial port device and the computer are connected correctly, and there is no problem with the connecting cable. You can try plugging and unplugging the serial connection cable again to ensure a firm connection.

2. Secondly, confirm that the computer has correctly installed the driver of the serial port device. You can check whether the serial device is displayed properly in Device Manager and there are no driver conflicts or problems.

3. Finally, open XCOM serial debugging assistant to ensure that the correct serial port number and other configuration parameters are selected in the settings.