To rule out potential issues, quickly test your individual components to ensure that they are working correctly individually, and are not the source of the problem:

• Serial cables
• Serial ports
• Serial devices

Test your components by:

• Hook up the serial cable(s), serial port(s), and serial device(s) in a different setup to see if the issue stems from a particular component, or the setup as a whole.
• Replace the serial cable, port, or device within your setup to further troubleshoot the issue’s origin.

When testing cables:

• Test each cable individually.
• Use short cables when you are testing.

When testing serial ports and devices:

• Press the Windows key + R, in Run, type devmgmt.msc, and press Enter to open the Device Manager. You can then check to see if your device is listed under Ports (COM & LPT).
• Ensure that the COM port number is the correct number for the serial device and that the software being used to connect the computer to the serial device uses the correct COM port number.
• If the device is listed with an error, follow the instructions on the website to reinstall the drivers.