Resolving COM Port issues
There are a few different things that have been known to cause a COM port error on the 578 Mobile. COM port errors are not as common on the mobile as they were with the handhelds, due to the fact that the mobile radio uses a direct USB connection and there is no additional software necessary for communication between the 578 and most computers.
With this in mind, a common error is the use of an incompatible version of Windows, which includes most versions of Windows which are older than Windows 7. As you know, the version of Windows you are using will need to support USB 2.0 or 3.0 in order to effectively communicate with your radio. If you are using an older PC, please consider using a more modern PC if you have one.
Improper installation of the CPS software can cause port conflicts, namely if the CPS software was not installed in "administrator mode". If you did not install the CPS program in "administrator mode", please uninstall CPS in control panel and then reinstall the program in "administrator mode" by right clicking the install icon and selecting "run in administrator mode". Also, once CPS is installed, it too should be run in "administrator mode".
A bad cable can be a problem as well. An inexpensive micro USB cable (like the kind typically used to link your PC to a Samsung phone) will suffice as a replacement if something has gone wrong with the supplied data cable. Stores such as Wal-Mart, HyVee, and Dollar General typically carry such cables for under $10.
Last but not least, something has actually gone wrong with your Windows operating system, and your PC is not detecting your radio via the USB port. Your PC could either have missing or corrupted USB drivers or DLL files which are causing a lack of communication between your PC and your radio. You can attempt to manually re-install these drivers from your PC manufacturer's website, or you can also use a third party piece of software such as Zadig USB Installer (AT YOUR OWN RISK) which re-installs the base set of USB drivers for most Windows platforms (including missing DLL files).
If this still does not work, please consider backing up your personal data and re-installing Windows.