I installed Rhino LED Dot Matrix Sign Board Software and based on the settings that I've tested, it appears that the software is working with the COM ports. This means you have to connect the display to the SERIAL port on the back of your PC. It's the long port with multiple holes. Once it's connected, go back to the software and then access Display > Port . Press on Test to check functionality. If it doesn't work, then replace the PORT number in the drop down menu.
Also, check the wire to be in good standing to see if it's not cut.