Hi, when trying to start Firefox, I get the message 'Process is already running.....'

1) The process is not running I have checked. 2) I have rebooted (numerous times.) 3) I have uninstalled Firefox and reinstalled and rebooted and the message still appears. 4) I have tried to find my lock file and have no idea what Charms are (Mozilla advice on finding the file to delete by hovering in the bottom right of the screen.) 5) I have entered the appdata string in my Start/Search and nothing is found.