well theres a few things you should do before trying to reinstall.. you need to make sure that you use "Add or Remove Programs" in your control panel to uninstall CA.. if you cant because a required file to uninstall has been removed, then you'll find yourself in a problem..
if you cant uninstall that way you have to make sure that the entire combat arms folders are removed.. including the NGM folder found NEXT TO the Nexon folder.. C:\NGM.. after that you need to remove all keys for Combat Arms out of your Registry.. to do that you need to use your "Run..." and use "regedit", then you need to search through the HKEY_LOCAL_MACHINE.. click the drop down on SOFTWARE, then the drop down on Nexon, and delete the folder Combat Arms
then re install