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We come across many common problems with the serial device configuration to the COM port. For instance the devices are not registered with the operating system. In similar situations, we should first check all the cables for loose connections. Secondly, we need to check the configuration of the port and then the resource conflict, if any.
Troubleshooting Steps
Ensure that the latest BIOS code is installed for your system (Check the motherboard manufacturer's website for updates). This will ensure proper operation of the ports to allow the ports to properly connect to and communicate with other devices.
Remove any cable extensions, or port sharing equipment between the computer system and the device.
Verify that the cable being used meets the specification for the device being connected. Try using a different cable that is known to be good, to rule-out cable issues.
Run a self-check test on the external device to ensure it is working properly. Connect the serial device to another serial port and see if it works. If it is fine, then the serial port is faulty.
See if the serial port device is working on a known good port. If it still does not work then the problem lies with the device and the same may have to be replaced.
Check if the COM ports are enabled, and properly configured in the BIOS Setup/Configuration Utility.
COM1 port should be tested first as this usually does not have a configuration problem or a resource conflict. If it is working fine and the others are not working then this might be due to a conflict in the resource, though it is quite possible that this is just because the software setup of the other port(s) is not correct.
